Office of Solid Waste
and Emergency Response
Washinaton DC 20460
SW-867
September 1982
Revised Edition
Evaluating Cover Systems
for Solid and
Hazardous Waste
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EVALUATING COVER SYSTEMS FOR SOLID AND HAZARDOUS WASTE
by
R. J. Lutton
U. S. Army Engineer Waterways Experiment Station
Vicksburg, Mississippi 39180
Interagency Agreement No. EPA-IAG-D7-01097
Project Officer
Robert E. Landreth
Solid and Hazardous Waste Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
DISCLAIMER
This report has been reviewed by the the Municipal
Environmental Research Laboratory U.S. Environmental Protection
Agency, and approved for publication. Mention of trade names
or commercial products does not constitute endorsement or
recommendation for use.
ii
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FOREWORD
The Environmental Protection Agency was created because of increasing
public and governmental concern about the dangers of pollution to the health
and welfare of the American people. Noxious air, foul water, and spoiled
land are tragic testimony to the deterioration of our natural environment.
The complexity of the environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is the first necessary step in problem solu-
tion; it involves defining the problem, measuring its impact, and searching
for solutions. The Municipal Environmental Research Laboratory develops new
and improved technology and systems to prevent, treat, and manage waste-
water and the solid and hazardous waste pollutant discharges from municipal
and community sources; to preserve and treat public drinking water supplies;
and to minimize the adverse economic, social, health, and aesthetic effects
of pollution. This publication is one of the products of that research—a
vital communications link between the researcher and the user community.
This report is to be used as a tool for evaluating various landfill
cover systems. This data information can be used in determining cover de-
sign requirements for compliance with the current regulations.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
111
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PREFACE
The land disposal of hazardous waste is subject to the requirements
of Subtitle C of the Resource Conservation and Recovery Act of 1976. This
Act requires that the treatment, storage, or disposal of hazardous wastes
after November 19, 1980 be carried out in accordance with a permit. The
one exception to this rule is that facilities in existence as of November
19, 1980 may continue operations until final administrative disposition is
made of the permit application (providing that the facility complies with
the Interim Status Standards for disposers of hazardous waste in 40 CFR
Part 265). Owners or operators of new facilities must apply for and receive
a permit before beginning operation of such a facility.
The Interim Status Standards (40 CFR Part 265) and some of the adminis-
trative portions of the Permit Standards (40 CFR Part 264) were published
by the Environmental Protection Agency in the Federal Register on May 19,
1980. The Environmental Protection Agency published interim final rules
in Part 264 for hazardous waste disposal facilities on July 26, 1982.
These regulations consist primarily of two sets of performance standards.
One is a set of design and operating standards separately tailored to each
of the four types of facilities covered by the regulations. The other
(Subpart F) is a single set of ground-water monitoring and response require-
ments applicable to each of these facilities. The permit official must
review and evaluate permit applications to determine whether the proposed
objectives, design, and operation of a land disposal facility will comply
with all applicable provisions of the regulations (40 CFR 264).
The Environmental Protection Agency is preparing two types of documents
for permit officials responsible for hazardous waste landfills, surface
impoundments, land treatment facilities and piles: Draft RCRA Guidance
Documents and Technical Resource Documents. The draft RCRA guidance
documents present design and operating specifications which the Agency
believes comply with the requirements of Part 264, for the Design and
Operating Requirements and the Closure and Post-Closure Requirements
contained in these regulations. The Technical Resource Documents support
the RCRA Guidance Documents in certain areas (i.e., liners, leachate
management, closure, covers, water balance) by describing current techno-
logies and methods for evaluating the performance of the applicant's design.
The information and guidance presented in these manuals constitute a
suggested approach for review and evaluation based on good engineering
practices. There may be alternative and equivalent methods for conducting
the review and evaluation. However, if the results of these methods differ
from those of the Environmental Protection Agency method, they may have to
be validated by the applicant.
iv
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In reviewing and evaluating the permit application, the permit official
must make all decisions in a well defined and well documented manner. Once
an initial decision is made to issue or deny the permit, the Subtitle C
regulations (40 CFR 124.6, 124.7 and 124.8) require preparation of either a
statement of basis or a fact sheet that discusses the reasons behind the
decision. The statement of basis or fact sheet then becomes part of the
permit review process specified in 40 CFR 124.6-124.20.
These manuals are intended to assist the permit official in arriving
at a logical, well-defined, and well-documented decision. Checklists and
logic flow diagrams are provided throughout the manuals to ensure that
necessary factors are considered in the decision process. Technical data
are presented to enable the permit official to identify proposed designs
that may require more detailed analysis because of a deviation from suggested
practices. The technical data are not meant to provide rigid guidelines
for arriving at a decision. The references are cited throughout the manuals
to provide further guidance for the permit officials when necessary.
There was a previous version of this document dated September 1980.
The new version supercedes the September 1980 version.
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ABSTRACT
A critical part of the sequence of designing, constructing, and main-
taining an effective cover over solid and hazardous waste is the evaluation
of engineering plans. Such evaluation is an important function of regulat-
ing agencies, and accompanying documentation can form one basis for issuing
or denying a permit to the owner/operator of the waste disposal facility.
This manual describes 39 steps in evaluation of plans submitted for appro-
val. Generally, the evaluator considers available soils, site conditions,
details of cover design, and post-closure maintenance and contingencies.
This report was submitted in fulfillment of Phase III of Interagency
Agreement No. EPA-IAG-D7-01097 between the U. S. Environmental Protection
Agency and the U. S. Army Engineer Waterways Experiment Station (WES). Work
for this manual was conducted during the period December 1979 to July 1980,
and work was completed in July 1980. Revisions have been made as appropri-
ate following a period of public review. Dr. R. J. Lutton, Geotechnical
Laboratory, WES, was principal investigator and author. Director of WES
during the work period was COL Nelson P. Conover, CE. Technical Director was
Mr. F. R. Brown.
vi
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CONTENTS
Foreword iii
Preface iv
Abstract vi
Metric Conversion Table viii
1. Introduction 1
Purpose and scope 1
Procedures of evaluation 1
Characterization of waste 2
2. Examination of Data 3
Test data review procedure (Steps 1-3) 3
Topographical data review procedure (Step 4) 13'
Climatological data review procedure (Steps 5-7) .... 16
3. Steps in Evaluation 20
Cover composition evaluation procedure (Step 8) .... 20
Thickness evaluation procedure (Steps 9-13) 24
Placement evaluation procedure (Steps 14-18) 29
Configuration evaluation procedure (Steps 19-20) .... 36
Drainage evaluation procedure (Steps 21-24) 43
Vegetation evaluation procedure (Steps 25-32) 45
4. Post-closure Plan 53
Maintenance evaluation procedure (Steps 33-35) 53
Contingency plan evaluation procedure (Steps 36-39). . . 55
References 57
vii
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METRIC CONVERSION TABLE
Multiply
By
To Obtain
acres
cubic feet per second
degrees (angle)
feet
feet per second
gallons (U. S. liquid)
inches
pounds (mass)
pounds (mass) per acre
pounds (mass) per cubic foot
square feet
tons (short, mass)
tons (mass) per acre
4046.856
0.02831685
0.01745329
0.3048
0.3048
0.003785412
0.0254
0.4535924
0.1120851
16.01846
0.09290304
907.1847
0.2241702
square meters
cubic meters per second
radians
meters
meters per second
cubic meters
meters
kilograms
grams per square meter
kilograms per cubic meter
square meters
kilograms
kilograms per square meter
vxn
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SECTION 1
INTRODUCTION
Growing concern for the preservation of a healthful environment, now
and in the future, was the major impetus to the enactment of Public Law
94-580, "Resource Conservation and Recovery Act of 1976" (21 October 1976).
An important part of solid and hazardous waste management is the regulatory
control exercised by the Environmental Protection Agency (EPA) regional
offices and corresponding agencies in state governments. In turn, a major
facet of this regulatory function is the evaluation of the adequacy of clo-
sure covers over the wastes.
PURPOSE AND SCOPE
This manual presents a procedure for evaluating engineering plans for
closure covers proposed for solid and hazardous waste land disposal facili-
ties. The manual is written principally for staff members in the Regional
EPA offices and/or state offices charged with evaluating applications from
owners/operators of solid and hazardous waste disposal areas. All aspects
of cover design are addressed in sufficient detail to allow for a complete
evaluation of the entire cover system. For more details on the subjects
covered in this manual, the reader is referred to a report emphasizing de-
sign and construction of covers which serves as the backup document.!
PROCEDURES OF EVALUATION
The evaluation of engineering plans should be performed with regard to con-
formance to applicable regulations. The sequence of procedures is outlined
as follows:
1. Examine soil test data
2. Examine topography
3. Examine climate data
4. Evaluate composition
5. Evaluate thickness
6. Evaluate placement
7. Evaluate configuration
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8. Evaluate drainage
9. Evaluate vegetation
10. Evaluate post-closure maintenance
11. Evaluate contingencies plan
The first three procedures in the evaluation process (presented in
SECTION 2) constitute a careful review of materials and conditions at the
proposed or existing site under consideration. Procedures 4-9 outline eval-
uations of the characteristics of the cover system within the constraints
offered by review procedures 1-3. Procedures 10 and 11 evaluate the ade-
quacy of the cover system and post-closure plan for future conditions, both
expected and unexpected.
Opportunity will be provided in the evaluation scheme in Section 2 for
consideration of departures from more or less conventional designs. Such an
option is specifically intended for instances where the owner/operator, for
one reason or another, proposes a design based on a special engineering
study or calculations. In evaluating such departures in design, the per-
mitting authority will find useful the additional technical guidance in Ref-
erence 1 or may enlist an experienced consulting firm or other source of
technical assistance to conduct the evaluation.
CHARACTERIZATION OF WASTE
Individual emphases among the procedures for examining and evaluating
covers are predicated to some degree on the characteristics of the waste to
be covered. Although not identified as such in this manual, the review of
waste characteristics can be considered a preliminary step from which the
examination proceeds. Accordingly, the reviewer may want to request docu-
mentation in the application. Some important characteristics of the waste
are composition (including water content), thickness, unit weight (in
place), prior compaction, gas-forming potential, and hazardous components.
The characterization of waste helps to identify the important func-
tions of the cover. Control of percolation often predominates as a cover
function but, even then, other functions should be recognized also and
ranked accordingly. Elsewhere, the control of percolation will be subor-
dinate to another function, e.g. control of gas migration. Reference 1 ad-
dresses each of the numerous functions of cover and should be helpful in re-
viewing this background for a specific site.
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SECTION 2
EXAMINATION OF DATA
TEST DATA REVIEW PROCEDURE
Sampling and testing are intended to characterize and delineate all
important soil types, and therefore should be under the direction of an ex-
perienced engineer or geologist having competence in the field of soil me-
chanics. Field sampling data and laboratory test results should be thorough
and according to widely accepted procedures. Table 1 summarizes the tests
that may be necessary.
Review Field Sampling of Soils Step 1
The objective of Step 1* is to establish that the applicant has satis-
factorily documented the physical characteristics, volume, and spatial dis-
tribution of each of the major, distinguishable soil types to be used as
cover. These data, obtained from test pits or borings in the borrow area,
must be accurate since the adequacy of the cover system and the feasibility
of the covering operation are directly affected.
The evaluation is accomplished by examining a map of soil sampling
locations along with some graphical or tabular presentation of the depths
and nature of the soils at each location. Soil types collected at each lo-
cation should be classified as described under Step 2. Soil type should be
identified at regular depth intervals even where the soil is obviously uni-
form to the depth of interest. Changes in soil types should be located.
Much of the delineation of soil types is accomplished on the basis of char-
acteristics observed and used in the field, e.g., color and feel when rubbed
between fingers. Such field characteristics should be explained and related
to the traditional U. S. Department of Agriculture (USDA) soil classes based
on grain size (Figures 1 and 2) where reasonable. Characterization in terms
of the Unified Soil Classification System (USCS) (Figure 3) is confirmed sub-
sequently in laboratory testing (Step 2).
The owner/operator application should include a brief description of
the field sampling methods besides the observations. The traditional manner
of exploring soil to depths of more than a few feet is by soil boring, but
trenching below ground surface or cleaning an existing bluff face or pit
* Step 1 may be unnecessary where the plan is to contract for the required
volumes of certain soil types delivered to the waste disposal site.
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TABLE 1. LABORATORY TEST METHODS FOR SOIL
Name of Test
Standard or
Preferred
Method*
Properties or
Parameters
Determined
Remarks/Special
Equipment
Requirements
Index and Classification Tests
Gradation Analysis
Percent Fines
Atterberg Limits
Specific Gravity
Soil Description
ASTM D421
D422
D2217
ASTM D1140
ASTM D423
D424
D427
ASTM D854
ASTM D2488
Soil Classification ASTM D2487
Particle size
distribution
Percent of weight
of material finer
than No. 200 sieve
Plastic limit, liquid
limit, plasticity
index, shrinkage
factors
Specific gravity or
apparent specific
gravity of soil
solids
Description of soil
from visual-manual
examination
Unified soil classi-
fication
Can usually be
estimated closely
Moisture-Density Relations
Dry Unit Weight
Water Content
Relative Densityt
Compaction
Reference 3 Dry unit weight
(dry density)
ASTM D2216
D2974
Water content as
percent of dry weight
Reference 3 Maximum and minimum
density of cohesion-
less soils
ASTM D698
(or 5- to
15-blow mod-
ification)
Optimum water and
maximum density
Both undisturbed
and remolded
samples
Modified test may
be substituted
for test with
vibratory table
Method for earth
and rock mixtures
is given in
Reference 3
(continued)
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TABLE 1. (continued)
Standard or
Preferred
Name of Test Method--
Properties or
Parameters
Determined
Remarks /Special
Equipment
Requirements
Consolidation and Permeability
Consolidationt
Permeability
ASTM D2435 One-dimensional
compressibility,
permeability of
cohesive soil
ASTM D2434 Permeability
Physical and Chemical Properties
Mineralogyt
Reference 4 Identification
of minerals
Organic Content
Reference 5
ASTM D2974
Soluble saltst
Pinhole Testt
Reference 6
Organic and
inorganic carbon
content as percent
of dry weight
Concentration of
soluble salts in
soil pore water
Reference 7 Dispersion tendency
in cohesive soils
Requires X-ray
diffraction
apparatus. Dif-
ferential thermal
analysis apparatus
may also be used
Where organic
matter content
is critical,
D2974 results
should be
verified by
wet combustion
tests (Reference 5)
Significant in
evaluation of
potential erosion
or piping
Shear Strength and Deformability
Unconfined
Compressiont
ASTM D2166
Undrained shear
strength
Applicable to
cohesive soil
only
(continued)
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TABLE 1. (continued)
Name of Test
Standard or
Preferred
Method*
Properties or
Parameters
Determined
Remarks/Special
Equipment
Requirements
Direct Shear,
Consolidated-
Drainedt
Triaxial Compres-
sion, Unconsoli-
dated-Undrainedt
Triaxial Compres-
sion, Consolidated-
Undrainedf
ASTM D3080
ASTM D2850
Reference 3
Effective shear
strength parameters,
cohesion and angle
of internal friction
Undrained shear
strength parameters,
cohesion and angle of
internal friction
Undrained shear
strength parameters,
cohesion and angle
of internal friction
Effective shear
strength param-
eters obtained if
pore pressure is
measured
* ASTM standard methods are given in Reference 2.
t Specialized test assigned only to obtain input for special engineering
analysis and design.
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100
10
Sand — 2.0 to 0.05 mm. diameter
Silt —0.05 to 0.002 mm. diameter
Clay — smaller than 0.002 mm. diameter
100 90 80 70 60 50 40 30 20
10
90
100
Figure 1. USDA textural classification chart.
Sieve openings in inches U.S. Standard Sieve Numbers
3 2 1'A 1 3A Vi Vt 4 10 20 40 60 200
I I I I I I I I I I II I I I IN I I I
USDA
uses
GRAVEL
SAND
Veryl 1 ... 1 r 1 Very
coafseF°arse| Wed | Flne | fine
SILT
CLAY
GRAVEL
Coarse | Fine
SAND
Coarse
Medium 1 Fine
SILT OR CLAY
i i i i nun MI i
J 1LJ LJ
1 f 0.42 0.25 Ol7
iii
i i
i i
100 50
10
1 0.42 0.25 0.1 / 0.05 0.02 0.01 0.005
0.5 0.074
Grain size in Millimeters
0.001
Figure 2. Comparison of USCS and USDA particle-size scales.
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Major Divisions
1
Fine-grained Soils I Coarse-grained Soils
tore t-h.m >mif of m-aterlal is aaaller than No. 200 sieve size.] More than half of Material IB larger than Ho. 200 sieve alze.
Baallest particle visible to the naked eye.
a
d
M
S
•
f
5
i
£
g
2
Gravels
More than half of coarse fraction
is larger than Ko. 1* sieve clxe.
•In. Bice My be uaed as equivalent
aleve alze)
Hi]
1 11
San
More than half of
la smaller than Ro
(For visual classl
Clean Gravels
(Little or no
flnea)
CimTela vlth
nnes
(Appreciable
aaount
of flnea)
}fl
is»
*M
' 8 t SC
rr*
ra *-f
t. a
3 -R
i»i
3 !i
CD M
R 3R
A * c
" 3S
lit
Highly Organic Soils •
Croup
Symbols
3
OH
OP
in
QC
sv
ST
m
sc
ML
CL
OL
HI
CH
OB
Ft
Typical Barnes
It
veil-graded gravels, gravel -aand mixtures,
little or no fines.
Poorly graded gravels or graval-aand mixtures
llttl* or no fines.
Sllty gravels, gravel -aand-ailt mixture.
Clayey gravels, grav»l-aand-elay mixtures.
Well -graded aanoa, gravelly sends, little or
no fines.
Poorly ended aands or gravelly sands, little
or no flnta.
Slltjr sands, sand-silt mixtures.
Clayey sands, sand-clay mixtures.
Inorganic silts and very fine sands, rock
flour, allty or clayey fine aanda or
clayey silts vlth slight plasticity.
Inorganic clays of lov to medium plaatlcity,
gravelly clays, sandy clays, allty clays,
lean clays.
Organic allta and oxmaalc allty clays of lov
plaatlclty.
Inorganic allta, mleaceoue or dlatonaeeoua
fins sandy or sllty soils, elastic allta.
Inorganic clays of high plasticity, fat clays.
Organic clays of medium to high plaatlclty,
organic sllta.
Paat and other highly organic soils.
Field Identification Procedures
(Excluding particles larger than 3 In.
and baaing fractions on estimated velghte)
5
Hide range In gram sizes and substantial
aatounts of all interoedlate particle sizes.
Predominantly one site or a range of sizes vlth
some Intermediate sizes missing.
Honplastle fines or fines vlth lav plasticity
(for* identification procedures see ML belov) .
Plastic fines (for Identification procedures
see CL belov).
Hide range in grain size and substantial amounts
of all Intermediate particle sizes.
predominantly one aica or a range of sizes
with some Intermediate sizes missing.
•onplastlc floss or fines vlth lov plasticity
(for Identification procedures see ML belov).
Plastic fines (for identification procedures
see CL belov).
Identification Procedures
on Fraction Smaller than Ho. ItO Sieve Size
Dry Strength
(Crushing
character! sties)
lone to slight
NldlUB to high
Slight to
madlum
Slight to
medium
High to vary
high
Medium to high
Dilatancy
(Reaction
to shaking)
gulck to slov
Rone to very
slov
Slov
Slov to none
Hone
Hone to very
slov
Toughness
(Consistency
near PL)
Rone
Mediun
Slight
Slight to
medium
High
Slight to
medium
Readily identified by color,. odor, spongy feel
and frequently by fibrous texture.
(1) Soils possessing characteristics of tvo groups are designated by combinations of group symbols. For example Gtf-GC, veil-
graded gravel-sand mixture vlth clay binder. (2) All sieve sizes on this chart are U. S. standard.
FIELD IDENTIFICATION PROCEDURES FOB FIRE-GRAINED SOILS OR FRACTIONS (MINUS SO. kO SIEVE)
Screening Is not intended; simply remove by hand the coarse particles that interfere vlth tests.
DllatancY (reaction to shaking). After removing particles larger than No. llO sieve size, prepare a pat of moist soil vith a volume
of about one-half cubic inch. Add enough vater If necessary to make the soil soft but not sticky.
Place the pat in the open palm of one hand and shake horizontally, striking vigorously against the other hand several times. A
positive reaction consists of the appearance of vater on the surface of the pat vhich changes to a. livery consistency and becomes
glossy. When the ssmple is squeezed betveen the fingers, the vater and gloss disappear from the surface, the pat stiffens, and
finally it cracks or crumbles. The rapidity of appearance of vater during shaking and of Its disappearance during soueezinn
assist In identifying the character of the fines in s soil.
Very fine clean sands give the quickest and most distinct reaction vhereas a plastic clay has no reaction. Inorganic silts such
as a typical rock flour, show a moderately quick reaction.
Dry Strength (crushing characteristics). After removing particles larger than No. lio sieve size, mold a pat of soil to the consis-
tency of putty, adding vater if necessary. Allov the pat to dry completely by oven, BUD, or air-drying, and then test Its
Figure 3. Summary of the USC system.
(continued)
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Information Required for
Describing Soils
6
Par undisturbed soils add information
on stratification, degree of compact-
ness, cementation, moisture conditions,
and drainage characteristics.
Give typical name; indicate approximate
percentages of sand and gravel, maxi-
mum site; angularity, surface condi-
tion, and hardness of the coarse
grains; local or geologic name and
other pertinent descriptive informa-
tion; and symbol in parentheses.
fcraimjjft ;
Sllty sand, gravelly; about 200 hard,
angular gravel particles 1/2-ln.
maximum size; rounded and aubangular
•and grains, coarse to fine; about 15$
nonplastic fines with low dry strength,
well compacted and moist in place; al-
luvial sand; (SH).
For undisturbed soils add information
on structure, stratification, con-
sistency in undisturbed and re-
molded states, moisture and drain-
age conditions.
Give typical nane; Indicate degree and
character of plasticity; amount and
Timrlm'ff" size of coarse grains; color
in wet condition; odor, if any; local
or geologic name and other pertinent
descriptive information; and symbol
In parentheses.
Example ;
Clayey •il'tj brown; slightly plastic;
snail percentage of fine sand;
numerous vertical root holes; fira
and dry in place; loess; (ML).
Laboratory Classification
Criteria
7
tions as given under field identification.
*"
•X"
-X"1^
^
tf
jX'
f
0 10 1 20 30 ItO 50 60 70
LIQUID LOOT
PLASHCIW CHART
For laboratory claiilflcatlon of fine-grained
1 — -*
/*
\^
,Jr
X
x^
/ A 1^"*
ao 90 loo
aoll<
strength by breaking and crumbling between the fingers. This strength Is a measure of the character and quality of the colloi-
dal fraction contained In the soil. The dry strength increases with increasing plasticity.
High dry strength is characteristic of claya of the CH group. A typical Inorganic silt possesses only very slight dry strength.
Silty fine sands and silts have about the same slight dry strength, 1>ut can be distinguished by the feel when powdering the
dried specimen. Fine sand feels gritty whereas a typical silt has The smooth feel of flour.
Toughness (consistency near plastic limit). After particles larger than the No. Uo sieve size are removed, a specimen of soil
about one-half inch cube in size is molded to the consistency of putty. If too dry, water must be added and if sticky, the
specimen should be spread out in a thin layer and allowed to lose some moisture by evaporation. Then the specimen is rolled
out by hand on a smooth surface or between the paJjns Into a thread about one-eighth inch In diameter. The thread is then
folded and rerolled repeatedly. IXiring this manipulation the moisture content is gradually reduced and the specimen stiffens,
finally loses its plasticity, and crumbles when the plastic limit Is reached.
After the thread crumbles, the pieces should be limped together and a slight kneading action continued until the lump crumbles.
The tougher the thread near the plastic limit and the stlffer the lump when it finally crumbles, the more potent is the colloi-
dal clay fraction in the soil. Weakness of the thread at the plastic limit and quick loss of coherence of the lump below the
plastic limit indicate either inorganic clay of low plasticity, or materials such as kaolin-type clays and organic clays which
occur below the A-line.
Highly organic clays have a very weak and spongy feel at the plastic limit.
Figure 3. (continued)
-------
wall may be as effective and less costly where on-site equipment is suffi-
cient. Whatever the method, it should be documented in the application.
The evaluator must decide whether the arrangement and spacing of sam-
ples have been adequate to delineate the vertical and lateral extent of the
major soil types. Where the evaluation indicates that sampling intervals
are too large, it may be necessary to require additional samples at inter-
mediate positions. One effective technique is to sample at fairly close
spacing along a single line across the borrow area. Elsewhere in the area
there may be a need for only a few additional borings to confirm that the
stratification (including thicknesses) along the cross section apply else-
where also. A grid pattern may also be definitive. The following example
helps to clarify Step 1.
Example: Suppose an application presents as an inclo-
sure the plan map in Figure 4. The sampling methods at
the three locations have been reviewed -and found to be
satisfactory; a drilling inspector made depth measure-
ments and identified and sampled the soil types. The
evaluator observes that one of the three sampling loca-
tions is distinct from the other two. The evaluator
therefore recommends that new boring locations be added
to delineate the extent of the CL soil more confidently
since this soil type is important in design of the
particular cover.
B-1 B-2 B-3
CL
CL
BOUNDARY OF
BORROW AREA
CL
SW
200'
Figure 4. Hypothetical cover soil source.
Check Adequacy of Soil Testing Program
Step 2
Two major aspects of the testing program that need to be evaluated are
the selection of tests and the adequacy of testing facilities and personnel.
Tests that might be expected or perhaps even specified as minimum require-
ments for all diagnostic samples are as follows:
10
-------
Grain-Size Distribution (Figure 5)
Percent Fines
Atterberg Limits
Soil Classification
Water Content
90
80
fe 70
>
00 60
CC
UJ
IBO
H
5 40
o
cc
£ 30
20
10
n
•"• —
_
SANDY SILTY CLAY (CD
Ceuli
W =
LL
PL
PI =
ana, w«
- 30 5%
40.0%
21.0%
= 19.0%
~~\
^x
N
\
\
\
\
\
\^
^^
100
10
1 0.1
GRAIN SIZE IN MILLIMETERS
0.01
0.001
Figure 5. Gradation of a landfill cover soil.
The tests may be required in duplicate (or more) for better, representation
and checking. These tests are basically indexing tests but also useful for
establishing the uniformity or variability within individual soil types.
Other important tests are compaction (Figure 6) and permeability. Even one
of these additional tests or test series may be adequate to establish char-
acteristics of the unit as a whole provided that unit is relatively uniform
in its index properties.
The remaining soil tests (Table 1) are assigned only where special
problems of slope stability, consolidation, etc., are anticipated. The need
for these tests may not become apparent until after most of the routine
index testing has been accomplished, sometimes not until the critical review
by the evaluator. Nevertheless, the lack of information from special tests
may occasionally constitute a basis for delaying a permit application.
Example: In reviewing a permit application an evaluator
finds that a county soil survey report has been used as
the basis for characterizing the soil at the proposed
11
-------
99
U.
3 97
96
95
94 —
93
i i r i
SANDY SILTY CLAY (CL)
CENTRALIA, WASHINGTON
•ZERO AIR
VOID CURVE
(Gs = 2.64)
OPTIMUM WATER CONTENT 22.2%
MAXIMUM DRY DENSITY 96.7 PDF
17
18
19 20 21 22 23 24 25
WATER CONTENT, PERCENT OF DRY WEIGHT
26
27
Figure 6.
Standard compaction test results with landfill
cover soil.*
29
borrow area. The applicant has used Atterberg limits,
classification, and grain-size distribution data from
the report for type Grenada 6 soil which has been mapped
over 36 percent of the county and specifically is shown
as underlying the borrow area. , After careful considera-
tion, the evaluator requests that several deep soil bor-
ing samples from the borrow area be tested at a quali-
fied testing laboratory to verify or reject the suit-
ability of the data from the general county report for
cover design. These samples will also serve to show how
well the county survey of surficial agricultural soils
represents the soils at depths below a few feet which,
of necessity, will contribute to total cover soil volume.
Check Soil Volumes Available
Step 3
At some stage, not necessarily when the site or borrow area is sampled
and tested, the sufficiency of cover soil volume should be evaluated. Accu-
rate volume calculations depend upon accurate measurements of soil thick-
nesses and areas. Accordingly, the evaluator may recommend additional sam-
pling locations, not only for a better fix on soil indices and properties
but to allow a better calculation of the volumes. Where the data in the
application have shown a uniformity of soil type, it may only be necessary
12
-------
to check thicknesses rather than to sample and test also. The following
example illustrates the situation, but also see the example under Step 1.
Example: An applicant has submitted the information
shown in Figure 7 as a basis for his estimates of vol-
umes of soil types available for use as cover. The
evaluator reasons that there is a possibility of a
sizable overestimation of suitable soils available to
complete the closure since variations of layer thick-
nesses between the existing sample locations are a
distinct possibility (shown by dashed line in the fig-
ure) . In this hypothetical case, the evaluator chooses
to accept the estimated volumes on the basis of observa-
tions he has made in a field inspection and after consul-
tation with a staff geologist.
An important factor in checking volumes available can be the bulking
factor. Some natural soils, particularly those at depth, have a relatively
high unit weight in situ. After excavation, working, and placement as cover
over solid waste, these soils will have experienced a reduction in unit
weight, i.e., a bulking effect, and available volumes tend to be underesti-
mated. In contrast, other soils, particularly those near the surface, have
a relatively low unit weight in situ so that available volumes are easily
overestimated. The evaluator should carefully check the basis for any bulk-
ing factor where soil is in short supply.
TOPOGRAPHICAL DATA REVIEW PROCEDURE
Examine Configuration and Topography Step 4
Next the surface configuration of the cover is examined to assure that
evaluations can be made in regard to slope stability, water erosion, and
wind erosion. Most engineered fills for highways, foundations, and so forth
are designed on the basis of accurate topography or multiple cross sections,
and the evaluator may reasonably expect some such basic data to accompany
the closure plan. Otherwise, the justification for omitting such basic data
should be convincingly presented in the application or be self-evident.
One basic form of data presentation is with cross sections through the
cover extending across the site (see Step 1). Cross sections should show
thickness of the closure cover and solid waste and the limits of natural
soil previously excavated for use as cover. Besides being useful for engi-
neering design and for evaluation of the design, cross sections are poten-
tially useful for monitoring changes in configuration that may take place as
a result of settlement in the long term. Preparation of cross sections is
well within the capability of most organizations engaged in construction and
can reasonably be expected as a part of an application.
A set of cross sections, often parallel to one another, can be highly
useful. Ordinarily the line of section (the surface trace of the cross sec-
tion) should trend downslope. Since many solid waste landfills will be com-
pleted with a somewhat irregular surface configuration approaching natural"
13
-------
200 FEET
BORINGS ARE PLOTTED SIDE BY SIDE BELOW
TO FACILITATE COMPARISON OF VOLUMES AVAILABLE.
SP
CH "" -•
^x
CL>
SP CL
"CH
ML
"T^sp
??
SP r«'v^
*
CH
ML
CL,.^-*
CH
ML
CH
Figure 7- Hypothetical cover soil volume data.
14
-------
hills and swales, it may be necessary for the cross sections to be oblique
to one another rather than parallel. About the only criterion for evalu-
ating sufficiency in the number of cross sections is whether they present
the important aspects of the surface form, closure cover, and underlying
solid waste.
Example: Suppose that the configuration of a solid
waste landfill is as shown in Figure 8. The owner/
operator of the landfill is seeking permission to place
final cover and move his current operations to an adja-
cent site. He has supplied the sketch of the site and
the surveyed cross section as the only graphical infor-
mation of the actual layout at the site. In his evalua-
tion, the staff member of the permitting authority feels
there are insufficient data on the existing configura-
tion, i.e., the base on which cover will be placed, and
he requires the applicant to provide another cross
section based on field measurements across the west
side. The evaluator has reasoned that the west edge of
the landfill near the drainageway is steeper and other-
wise distinct from the large open side on the south and
therefore should be represented accurately and sepa-
rately in cross section for special examination.
SURVEY POINTS ON
EXISTING SURFACE
100 FEET
Figure 8. Hypothetical landfill configuration.
15
-------
CLIMATOLOGICAL DATA REVIEW PROCEDURE
Examine Precipitation Records
Step 5
The application should include data on the precipitation to be ex-
pected at the site. A useful record typically gives average amounts for a
period of at least several years in the past, e.g. the average monthly pre-
cipitations from the last 20 years or thereabout. Average data can be sup-
plemented with typical records of rainfall on a daily or even hourly basis
for a better picture of rainfall distribution in detail. The source of all
climatological data should be given also so that verifications can be made.
Figure 9 is a map of average annual precipitation that the evaluator can use
to check roughly the expected annual precipitation provided by the appli-
cant. Similar information is available for Alaska and Hawaii. In some moun-
tainous or coastal regions the average rainfall can vary over short dis-
tances, and special care must be exercised in evaluation as illustrated by
the following example.
Figure 9. Average annual precipitation in inches (US Dept of Agriculture)
Example: Precipitation records provided in the permit
application concerning a landfill for a city in the
Pacific Northwest are those compiled from the downtown
weather station. The evaluator recognizes that there is
a difference in the weather at the downtown location
(near sea level) and the weather at the landfill which
16
-------
is located in foothills at the far end of the same
county. Therefore, he requests more representative data
or conclusive evidence that any departures will be on
the conservative side.
Examine Evapotranspiration Estimates
Step 6
Since evapotranspiration operates in an important manner to remove '
moisture from the cover, it must be regarded as a major factor in cover de-
sign. Therefore, an applicant should include in documentation an accurate
estimate of monthly evapotranspiration as evidence that this factor has been
included in the design. The source of information should be included also.
Where the evapotranspiration data have been derived through calculations
from other parameters, the calculations should be included and explained,
and references should be made to original sources. Figure 10 is a map of
average annual lake evaporation over the contiguous United States which the
evaluator can use to check roughly the expected annual evapotranspiration.
Evapotranspiration approximately equals lake evaporation which is about
0.7 x pan evaporation.
Figure 10. Average annual lake evaporation in inches,
according to the National Weather Service.
Examine Design Storms Step 7
Closure covers should be designed not only for average precipitation
17
-------
but also for high rates over short durations. Such information is readily
available in the form of design storms for any locality, and it is reason-
able to expect that the documentation accompanying an application recognize
several extreme rainfalls for recurrence intervals of possible interest.
For an average size landfill a 1-hour storm and storms of longer duration
are of typical interest. The recurrence interval would likely be 10 or
20 years, but the applicant should present reasons for choosing specific
intervals and storm durations. Figure 11 is an example of summary informa-
tion available to the evaluator for checking design storm amounts supplied
in an application.
Figure 11. Ten-year 1-hour rainfall in inches (US Weather Bureau)
A sequel to the presentation of design storm data is the calculation
of flood discharges for ditches and other elements of the drainage system.
The calculation in simplest form utilizes the rational equation:
where Q
JRO
A
Q = CRO ± A
= peak discharge, cubic feet/second
= runoff coefficient
= rainfall intensity, inches/hour
= area of basin, acres
18
-------
The formula above incorporates the approximation that 1 inch/hour/acre
= 1 cubic foot/second. Roughly approximated, the C^Q values for vegetated
clayey soils on flats and slopes are about 0.5 and 0.7, respectively, and
for vegetated sandy soils on flats and slopes are about 0.2 and 0.4.
19
-------
SECTION 3
STEPS IN EVALUATION
Steps in this section differ from those in Section 2 by involving ac-
tual evaluation of the designs and judgments submitted by the applicant
rather than just the examination and ordering of basic data.
COVER COMPOSITION EVALUATION PROCEDURE
The basis for evaluating the composition of the cover is the collec-
tion of data on quantities and descriptions supplied with the application.
Evaluate Composition Step 8
Referring to Table 2, the evaluator should check the soil composition
for suitability as cover by establishing the soil's strengths and deficien-
cies in a general way. Where a soil is rated IV or higher, look for special
design features to compensate for deficiencies (e.g., multilayering to sup-
plement a vulnerable soil with other types). Higher rating numbers tend to
indicate greater need for special features. There is need, of course, to
exercise good judgment when applying a somewhat subjective ranking as that
in the table.
In the particularly important function of minimizing infiltration, it
may be necessary to reject a simple cover design of one layer and require
inclusion of a clay soil layer or other barrier. This necessity may arise
where the dominant soil proposed as cover is:
a. Designated GW, GP, or SP by testing (see Figure 3)
b. Dispersive and therefore'possibly subject to internal erosion (see
Reference 1)
c. Insufficient in volume for cover design
Other options may be to import a more suitable soil type or in some way to
improve characteristics by additional treatments.
Example: According to the testing results accompanying
the permit application, cover at a solid waste disposal
site will consist of gravelly sand classified SW accord-
ing to the USCS. The permitting authority has previously
assigned a high priority to impeding water percolation
into the solid waste. The evaluator, therefore, notifies
20
-------
TABLE 2. RANKING OF USCS TYPES ACCORDING TO PERFORMANCE OF COVER FUNCTIONS
USCS
Symbol
GW
Typical Soils
Well -graded gravels, gravel-sand
mixtures, little or no fines
GP
GM
GC
SW
SP
SM
SC
ML
Poorly graded
sand mixtures
fines
Silty gravels
mixtures
gravels, gravel-
, little or no
, gravel-sand-silt
Clayey gravels, gravel-sand-clay
mixtures
Well-graded sands, gravelly
sands, little
Poorly graded
sands , little
Silty sands,
Clayey sands,
or no fines
sands , gravelly
or no fines
sand-silt mixtures
sand-clay mixtures
Inorganic silts and very fine
sands, rock flour, silty or
Go- No Go
(RCI Value)*
I
(>200)
I
(>200)
III
(177)
V
(150)
I
(>200)
1
(>200)
II
(179)
IV
(157)
IX
(lOlt)
Trafficability
Stickiness
(Clay, %)
I
(0-5)
I
(0-5)
III
(0-20)
VI
(10-50)
II
(0-10)
II
(0-10)
IV
(0-20)
VII
(10-50)
V
(0-20)
clayey fine sands, or clayey
Water Percolation
Gas Migration
Slipperiness Impede Assist Impede Assist
(Sand-Gravel, %) (k, cm/s)* (k, cm/s)* (H , cm)* (H , cm)*
1 X in
(95-100) (io"2)
I XII I
(95-100) (io"1)
III VII , VI
(60-95) (5 x 10 a)
V V, VIII
(50-90) (10" ) g
•H
II IX IV ^
(95-100) (10 J) o
£
ii xi ii £
(95-100) (5 x 10 ^ £
-P
IV VIII V $
(60-95) do""1) a
(0-55) (3 K 10"H) *
§
CO
VII
(0-60)
IX III X
(0-50) (10"')
X I
(6)
IX II
VII IV
(68)
IV VII
—
a
VIII III °
(60) |
to
VII IV £!
to
o
VI V a
(112) £
. V VI
tl
o
III VIII $
(180) -
3
ol
II IX «C
(180) 1
CO
soils, elastic silts
CH
Inorganic clays of high
plasticity, fat clays
OH
Organic clays
of medium to high
plasticity, organic silts
VI
(Ht5)
XI
(62)
X
(50-100)
X I XII
(0-50) (I0"y)
I X
(200-1*00+)
Pt
Peat and other highly organic
soils
XII
(continued)
-------
TABLE 2. (continued)
N3
Erosion Control
Reduce Freeze Action
USCS Fire Water Wind Dust Fast Freeze Saturation
Symbol Resistance (K-Factor)* (Sand-Gravel, %} Control (H , cm)* (Heave, mm/day)
GW
GP
GM
GC
SW
SP o
•rt
S
fcl
Kf
SM £
2
0]
oJ
c3
SC
10)
IX
(continued)
-------
TABLE 2. (continued)
N>
OJ
USCS Side Slope
Impede
Discourage Vector Discourage Support Future Use
Symbol Stability Seepage Drainage Burrowing Emergence Birds Vegetation Natural
GW
GP
GM
C C!
O O
•H -H
3 3
0 0
o a
sw jj | «
•p
OJ (U 01
•P -P -P
SP 7. 1 4
P> >* f*
^,
0 0) -P
aj CO -H
SM S § S
,0 M <
H h t.
o o
SC >
CL u 2 «
.3 § §
€ MM
0) C C
OL -P 33
Q C! fl
33
MH 11
§ 3
CO CO
CH
OH
Pt
X X
X X
VIII VI
p
•H
r-t
-H V V
Qj
U
-H
^ IX IX o
w -H
£ ta
CO t^
s ix ix a
C » "
-H H ^
I ii S u |
!n M P
W 0)
VI g III a
V M
^ H C
-33*
> III VII §
•a ^
a °>
"VI IV |
-H
^ II IV
I
CO
I VIII
VIII
Ill
Foundation
+j>
-H
H
•H
0)
•H
0)
EH
0
o
1
O
o
o
w
0)
Cfl
^
H
ct)
1
bO
1
0)
CO
* RCI is rating cone index, k is coefficient of permeability, H is capillary head, and K-Factor is the soil erodibility factor.
The ratings I to XIII are for best through poorest in performing the specified cover function.
-------
the applicant that the SW soil (well-graded sand) is
unacceptable (ranked IX in Table 2) in a single-layer
configuration and that it will be rejected unless a
layered system with a barrier layer is incorporated.
Example: The applicant at a site has proposed to use a
clayey silt for closure cover. The applicant had pre-
viously been asked to obtain at his own expense a series
of tests on the soil to determine its tendency towards
dispersion. The area has a high rainfall, and its low
topography can conceivably cause a detention of runoff
with increased opportunity for infiltration. Internal
erosion that can affect dispersive soils would conceiv-
3 ably lead to a deterioration of the cover by migration
of soil particles into the solid waste below. The
laboratory test report in the second submittal of the
application confirms that the silty soil has a modest
tendency for dispersion. The evaluator concludes that
inclusion of a clay barrier is advisable. However, the
evaluator goes on to explain that other solutions to the
potential problem may be investigated also since the
applicant has indicated an interest in treating the
dispersive soils with lime in order to flocculate clay
particles and reduce their tendency towards dispersion.
The susceptibility of particular soil types to surface erosion by
running water can also be evaluated according to a useful erosion loss equa-
tion (see Step 19).
THICKNESS EVALUATION PROCEDURE
The evaluation of closure cover thickness is often of primary impor-
tance and the evaluator should devote considerable attention to it. Thick-
ness in excess of a certain established minimum* may be governed by one or
more of the following factors:
a. Coverage
b. Infiltration
c. Gas migration
d. Trafficability and support requirements
e. Freeze/thaw or dry/soak effects
This list may be extended by addition of other factors of possible concern
such as:
* Minimum cover thickness requirements vary from state to state according
to experience.
24
-------
f. Cracking (factors f, g, h, and i are discussed in Reference 1)
g. Differential settlement and offset
h. Membrane protection
i. Vegetative requirements
Evaluate Coverage Step 9
The closure cover functions basically to cover solid waste completely;
therefore, some guidance is in order to evaluate for factor ji, above. A
reasonable criterion of adequacy for coverage over irregular solid waste can
be offered as follows:
T > 2R
where T is cover thickness and R is relief. The relief is defined for
this criterion as.the vertical distance from high point to low point of ir-
regularities on the top surface of the solid waste. The size of the area
over which this vertical distance should be measured corresponds roughly to
the size of the equipment used for placing closure cover. Where intermedi-
ate size dozers are to be used, the area within which the relief is measured
would be on the order of 20 by 20 feet. In large covering operations where
pans or other large pieces of equipment are to be used, the area size could
be on the order of 50 feet across.
The applicant may choose to circumvent the requirement of increasing
thickness above the established minimum to compensate for relief by smooth-
ing the upper surface of solid waste. Where sand fill is available, it can
be placed alone or mixed with heterogenous solid waste in roughly equal pro-
portions for a more workable material to achieve a smoother top surface.
The sand or the mixture thus forms a buffer1 that generally improves the
performance and longevity of the cover. This buffer also serves specifi-
cally as a base for more effective compaction of layers placed above.
Evaluate Thickness for Infiltration Step 10
Logically, the next criterion to be examined in the evaluation con-
cerns infiltration, J3_» above. Adequacy against infiltration can be evalu-
ated by use of a water balance technique in which input of water on a
monthly or daily basis is compared with expected losses from surface runoff
and evapotranspiration. Excesses beyond storage capacity of the cover soil
are considered to pass through the cover as percolation. The evaluator is
referred to another manual** in which the details of a recommended computer-
ized procedure are outlined step by step.
For purposes of evaluating the thickness of the cover, a somewhat ab-
breviated water balance technique may be useful also. This method has been
suggested for predicting percolation by the EPA,9 and its utility in evalu-
ating or designing cover has been reviewed.1 The water balance technique
serves to check the effect of increased thickness for providing increased
25
-------
water storage in the cover soil and consequent decrease in percolation. The
example below illustrates the technique and its use.
Example: Using a 30-year climate record, the evaluator
analyzes the effectiveness of a 2-foot silty sand cover
with grass at Chippewa Falls, Wisconsin. Table 3 shows
the water balance tabulation. The average annual perco-
lation is calculated to be 3.88 inches. The evaluator
next expands this analysis to explore the effects of a
much thicker cover on percolation. The result is shown
in Table 4. A storage capacity of 8 inches (represent-
ing greatly increased thickness) is substituted for the
storage of 1.05 inches used in Table 3. The overall
effect on cumulative percolation is small, with a reduc-
tion by only about 20 percent to an annual percolation
of 3.13 inches. His analysis indicates to the evaluator
that increasing cover thickness is not an efficient way
of reducing percolation in this area.
Evaluate Thickness for Gas Migration Step 11
Thickening the cover is sometimes a direct and effective procedure
along with choice of soil (Step 8) for reducing gas migration through the
cover, especially to the extent that increased thickness reduces evaporation
and preserves a high moisture content. The technique is particularly attrac-
tive for remedial work where problems are localized. Increasing the thick-
ness of coarse-grained soils decreases gas discharge directly when diffusion
is the mechanism. Where gas is driven through coarse soil by a difference
in total pressure, however, thickening the cover may be ineffective. In
fine-grained soils the open pore space necessary for migration by either
diffusion or pressure difference is at least intermittently blocked by the
included pore water, and the evaluator must consider this complication crit-
ically in arriving at his recommendations. Finally, there is the potential
problem of excessive lateral migration as a result of effective blockage of
vertical migration. For this condition, the evaluator will need to address
gas drainage in considerable detail (Step 24).
The generation of methane and carbon dioxide from wastes, followed
by migration driven by pressure difference, provides the opportunity for
any relatively minor but toxic gaseous components to be moved along as well.
Therefore, any capacity for generating gases in abundance greatly compounds
the problem of retaining hazardous gaseous chemicals and may make gas drain-
age imperative (Steps 15 and 24).
Example: The cover proposed for a solid waste disposal
site in a high-rainfall area consists of a fine-grained
soil that basically functions to exclude most percola-
tion. Anticipating eventual problems with gas migration
through this cover, the evaluator considers .recommending
thickening of the cover design. However, after careful
consideration, the evaluator concludes that adjustments
of the thickness will not have a dramatic effect because
26
-------
TABLE 3. MONTHLY WATER BALANCE ANALYSIS
IN INCHES FOR CHIPPEWA FALLS, WISCONSIN1
Parameter
Average Precipitation
(P)
Runoff (RO)
Moisture available for
infiltration (I)
Potential evapotrans-
piration (PET)
(I - PET)
(E neg (I - PET))
Soil moisture
storage (ST)
(AST)
Actual evapotrans-
piration (AET)
Percolation (PRC)
Jan
0.89+
0.00
0.00
0.00
1.05
0.00
0.00
0.00
Feb
0.71+
0.00
0.00
0.00
1.05
0.00
0.00
0.00
Mar
0.77*
0.77*
0.05
0.72
0.00
0.72
1.05i
0.00
0.00
0.72
Apr
2.55
0.17
2.38
1.10
1.28
1.05
0.00
1.10
1.28
May
3.73
0.2U
3.U9
2.50
0.99
1.05
0.00
2.50
0.99
Jun
U.19
0.27
3.92
3.90
0.02
(0)
1.05
0.00
3.90
0.02
Jul Aug
3.65 3.56
0.2k 0.23
3.U1 3.33
U.60 U. 00
-1.19-0.67
-1.19-1.86
0.27 0.13
-0.78-O.lU
It. 19 3.U7
0.00 0.00
Sep
3.37
0.22
3.15
2.70
O.U?
0.58
+O.lt5
2.70
0.00
Oct
2.0k
0.13
1.91
1.20
0.71
1.05
+O.U7
1.20
0.2U
Nov Dec
0.67* 1.00+
0.67*
o.oU
0.63 o.oo
0.00 0.00
0.63 o.oo
1.05 0.05
0.00 0.00
0.00 0.00
0.63 o.oo
Ann.
U.OU
2U.53
1.59
22. 9U
20.00
19.06
3.88
t Precipitation between November 16 and March 15 is listed as snow but is changed to runoff at
spring thaw.
* Precipitation in November and March is divided into half rain, half snow.
§ Water-holding capacity is assumed to be at maximum in March when snow melts.
TABLE 4. MONTHLY WATER BALANCE ANALYSIS IN INCHES WITH THICK COVER*
• —• •
Parameter Jan Feb Mar Apr May Jun Jul Aug Sep Oct Hov Dec Ann.
Average Precipitation 0.89+ 0.71+ 0.77* 0.67* 1.00+ k.Ok
(P) 0.77* 2.55 3.73 U.19 3.65 3.56 3.37 2.0k 0:67* 2U.5J
Runoff (RO) 0.05 0.17 0.2U 0.27 0.2U 0.23 0.22 0.13 O.OU 1.59
Moisture available ?°rQfQO 0>00 Q_72 2_3g 3^ 3_Q2 300 22^
infiltration (I)
Potential evapotrans- Q nQ Q^QQ 0_QO 1>10 2>50 3>90 ^g0 ^00 2>70 Ii20 0_00 0_00 20.QQ
piration (PET)
(I - PET)
(E neg (I - PET))
Soil moisture
storage (ST)
(AST)
Actual evapotrans-
piration (AET)
Percolation (PRO)
0.00
8.00
0.00
0.00
0.00
0.00
8.00
0.00
0 00
0.00
0.72
8.00S
0.00
0 00
0.72
1.28
8.00
0.00
1 10
1.28
0.99
8.00
0.00
2.50
0.99
0.02 -1.19-0.67
(0) -1.19-1.86
8.00 6.89 6.33
o.oo -1.11-0.56
3.90 U. 52 3.89
0.02 0.00 0.00
O.U5
6.78
+O.U5
2.70
0.00
0.71
7.U9
+0.71
1.20
0.00
0.63
8.00
+0.51
0.00
0.12
0.00
8.00
0.00
0.00
0.00
19.81
3.13
* Compare with Table 3.
t Precipitation between November 16 and March 15 is listed as snow but is changed to runoff at
spring thaw.
± Precipitation in November and March is divided into half rain, half snow.
§ Water-holding capacity is assumed to be at maximum in March when snow melts.
27
-------
the soil usually retains considerable moisture (depend-
ing on the complications of rainfall history and evapo-
transpiration1) and is already blocking most of the gas
movement. The evaluator learns that the applicant be-
lieves that thickening the cover to reduce the remain-
ing intermittent, uncontrolled gas discharge will also
not be cost-effective and, therefore, thickening is not
favored by the applicant. He then concentrates his
immediate attention on considering other options such as
gas vents though it may be necessary to return later to
the thickening technique despite its low
cost-effectiveness.
Evaluate Support Requirements Step 12
The low bearing capacity of some solid waste landfills can be circum-
vented by increasing soil thickness above waste. In this way, the rela-
tively strong soil resists punching and rotational shear. The thickness of
soil should be at least 1.5 x the width of footings. However, any proposal
to superimpose buildings on the cover should receive particularly critical
reviews and would ordinarily be rejected for a hazardous waste site. Past
experience with buildings on landfills is replete with cases of structural
damage from differential settlement and unnecessary hazard from accumulation
of methane and other gases.
Consider Freeze/Thaw and Dry/Soak Effects Step 13
In cold regions of the country, special attention may need to be di-
rected to disturbing effects of freezing. Similarly in semiarid areas sub-
ject to periods of sustained drying conditions, equal concern may be war-
ranted in regard to excessive drying and cracking. The reasons for concern
have been summarized elsewhere 1 but largely involve substantial decreases in
effectiveness of cover in impeding water and gas migration.
The evaluator may check for adequacy of the cover thickness by use of
Figure 12 or similar summary. In case of a need for greater detail or in
locations of mountainous terrain where the depth of freezing can vary over
short distances, the evaluator should seek information on depth of freezing
from a local agricultural agency. The depth of drying to be expected over
extended droughty periods can similarly be estimated on the basis of experi-
ence in the region.
Example: An applicant has proposed to use 3 feet of
soil in the northern Great Plains where the average
annual maximum depth of freezing is 3 feet. To avoid
disturbance of the cover to its full thickness the
evaluator recommends that cover thickness be increased
to 4 feet.
Before requiring substantial modification by thickening the cover, the eval-
uator would ordinarily obtain the opinion of one or more local geotechnical
engineers regarding the disturbance of the cover.
28
-------
Figure 12. Regional depth of frost penetration in inches.
PLACEMENT EVALUATION PROCEDURE
11
After selection of the material and appropriate thickness for cover,
efforts should be directed to the most effective placement and treatment.
Cover can be improved in several ways as it is constructed. Materials may
be added for better gradation, hauling and spreading equipment can be oper-
ated beneficially, and certain layering can be introduced.
Evaluate Cover Compaction
Step 14
Some compaction is almost always accomplished during the spreading of
cover soil; and this densification is highly effective in producing bene-
fits, principally increasing strength and reducing permeability. Figures 13
and 14 illustrate these effects and provide the evaluator some guidance on
what can be achieved. The laboratory compaction test provides a useful data
base on which the evaluator can judge the effects of compaction of the cover
under consideration. It has been found1 that soil compacted routinely over
soft waste (municipal wastes) falls below standard compaction curves such as
obtained in ASTM D698 (Table 1). The differences in field compaction re-
sults over spongy solid waste versus those over a hard base can be compen-
sated approximately by using laboratory test procedures with fewer than the
29
-------
DC
o
u
y
ec
U.
OS
IU
H
*
U
FltOH
CFFCCTIVf STtCSS
FtlLUHC CHVCLOPCi
APPKOXIHtTC COKHCUTICK
IS FOK COHCSIOHLCSS
UATCKItLS WITHOUT —
FUSTIC FIHES
1.2 I.I 1.0 03
25
JO
100 110 120
DRY UNIT WEIGHT (yD), PCF
Figure 13. Relation of effective angle of internal
friction to dry unit weight for cohe-
sionless soils (US Navy).
Figure 14. Coefficient of permeability of materials as affected
by degree of compaction.
30
-------
"standard" 25 blows of the compacting hammer. Keep in mind that the objec-
tive of the laboratory tests is to model actual field compaction of cover
soil with dozers and other compacting equipment.
Approximate general guidance (Figure 15) has been derived regarding
the field compaction effort necessary in 6 to 12 inches of soil cover on
municipal solid waste. Field dry density of the cover can be predicted from
measured placement water contents by using laboratory compaction curves at
appropriately light compaction effort. For example, where a dozer makes
four passes on the average, a 5-blow compaction curve should be determined
by laboratory testing and be used for predictions. The curves shown in
Figure 15 appear generally valid, but relations between field compaction and
laboratory curves should be determined site-specifically if cover density
data are deemed necessary;1 the evaluator may need to make this judgment
under Step 2. A reasonable goal for which one might strive, particularly in
the compaction of barrier layers, is 90 percent of maximum dry density ac-
cording to 5- or 15-blow compaction tests. On the other hand, when
105
u.
U95
z
111
Q
90
85'
80
10
15 20 25
WATER CONTENT, % OF DRY WEIGHT
30
35
Figure 15. Schematic guidance for predicting cover compaction
results with intermediate-size dozers on municipal
solid waste using laboratory test results.
31
-------
compacting on a solid base, e.g., on a granular soil-like solid waste, one
might strive for 90 percent of maximum dry density by standard 25-blow
tests.
Example: In his second submission of an application, an
owner/operator has included results of 15-blow compac-
tion tests conducted on the cover soil by a certified
testing laboratory (Figure 16). It is claimed later
that approximately 90 percent of maximum dry density
will be achieved with six passes of the compacting
equipment. The natural water content is approximately
10 percent. The evaluator notes that the cover soil is
to be excavated and hauled and placed directly. There-
fore, he asks the applicant to expand on his intentions
as far as manipulating the water content of the soil
closer to optimum in order to reasonably expect 90 per-
cent of maximum dry density.
100
95
90
GO
LU
O
85
80
75
OPTIMUM WATER
CONTENT = 27%
7^ ana/ KH A v I
• I
10 15 20 25 30
WATER CONTENT, %
35
40
Figure 16. Hypothetical cover soil compaction.
Evaluate Internal Layering
Step 15
Layering is a promising technique for final solid waste cover. By
combining two or three distinct materials in layers (Figure 17) the designer
may mobilize favorable characteristics of each together at little extra ex-
pense. The following descriptions* should help to guide the evaluation of
layered cover designs.
The primary feature in layered systems is usually the -barrier. This
layer functions to restrict passage of water or gas. Barrier layers are
32
-------
: LOAM
B ARR ER)
SILT (FIL ER)
i||jijiijl;;j!l!jjj SAND (BU
(BUFFER
v//////////,
Figure 17. Typical layered cover system.
almost always composed of clayey soil that has inherently low permeability;
USCS types CH, CL, and SC (Figure 3) are recommended. Soil barriers are
susceptible to deterioration by cracking when exposed at the surface, so that
a buffer layer above is recommended to protect the clayey soil from exces-
sive drying. Similarly, where a synthetic membrane is used as the barrier,
buffer soils are needed above and below the membrane for its protection.
Synthetic membranes of butyl or neoprene rubber, hypalon, polyolefin,
polyvinyl chloride, etc., may be considered in place of soil barriers.1
Usually a sheet thickness of at least 20 mils is required. Some membranes
should be spread carefully over a smooth base to lie in a relaxed state or a
5-percent slack may be necessary; usually the manufacturers provide direc-
tions. Soils immediately above and below a membrane can constitute critical
components of the layered cover since irregularities and hard pieces imping-
ing on the membrane can cause damage, particularly luring subsequent compac-
tion. Therefore, the application should address thoroughly the question of
preserving the integrity of the impermeable membrane during construction.
Manufacturer's recommendations for splicing the membrane in the field or in
the shop should be followed and should be detailed in the application. Pro-
vide a trench at least 8 inches deep or other anchorage at the top of any
slope. The evaluation of synthetic membranes in layered cover systems may
benefit from related guidance on basal liner systems presented in another
manual;12 particularly in regard to reactivity between waste and membrane.
Experience in using membrane liners within cover has emphasized the
need for special attention to lateral drainage of the water that accumu-
lates. Water trapped by the liner may saturate the protective soil above
and make it vulnerable to erosion. On slopes over about 10 percent, a few
heavy rainstorms may erode such soil and expose the liner in channels. A
further consequence of saturation is damage to the roots of vegetative cover
after a few days of submergence. Consequently, the evaluator should check
for attention to these concerns where a membrane is planned for incorpora-
tion in the cover. A system of pipe drains buried along lines of drainage
convergence is one possible solution to potential saturation problems.
Barrier layers may also be constructed by adding certain additives or
cements to the available soil. Addition of bentonite clay is a proven means
33
-------
of reducing permeability, but homogenizing the mixture can present difficul-
ties and may need to be confirmed by laboratory tests, post-placement exami-
nation, or other means identified in the permit application. Other addi-
tions to soil, such as lime, portland cement, and bituminous cement, may re-
quire an even more conservative stance on the part of the evaluator since
experiences with these materials in layered covers are quite limited.
Layered cover systems should include buffer soil layers where a buffer
layer may be described as a random layer having a subordinate covering func-
tion. Buffers serve to protect the barrier layer or membrane sheet from
tears, cracks, offsets, punctures, and other deterioration. Below a barrier
or the main cover soil a buffer also provides a smooth, regular base. Any
soil type will serve as a buffer ordinarily, but it should be free of clods.
A properly placed buffer filling voids around barrels of waste serves to
minimize settlement and disruption of the final capping cover.
Where soils of widely different grain size are in contact, there may
be a tendency for fine particles to penetrate the coarser layer. As a re-
sult, the effectiveness of coarse layers that may be used for water drainage
can be reduced by clogging of the pores. Removals from the fine layer may
promote additional undesirable effects, such as internal erosion and settle-
ment. Similar problems can develop around pipe drains buried in the cover
system. Such problems can be eliminated by selecting the proper size grada-
tion of one or both of the soil layers. The coarser soil layer is commonly
termed as the filter. A widely used criterion is written
D, (filter soil)
n ,f. rrpr- < 4 tO 5
Doc(finer soil)
OJ
where D-j^ and 035 refer to the grain sizes for which 15 and 85 percent by
weight of the soils are finer, respectively. Common filter soils are SP,
SM, SW, and GW (Figure 3); filter fabric or cloth may be considered in place
of a soil filter layer.
Example: Suppose that grain-size distribution curves »
have been submitted with the application to represent
soils to be used in a layered system. The evaluator
locates the Dj5 and 035 grain sizes at the points shown
in Figure 18. Since the ratio of these sizes does not
meet the criterion, the application is returned for
modification of design.
A water drainage layer, blanket, or channel may be designed into cover
in numerous ways to provide a path for water to exit rapidly. Well-sorted
(poorly graded) sand and gravel are recommended as effective drainage mate-
rials, i.e., soils classified GP and SP. Drainage channels and layers may
be associated with a system of buried pipe drains, but the expense of this
combined system ordinarily limits its applicability to high-priority dis-
posal areas.
34
-------
100
1 0.1
GRAIN SIZE IN MILLIMETERS
0.01
0.001
Figure 18.
Hypothetical size gradation of ineffective
filter soil.
Gas drainage layers and channels may have granular consistency and
interconnections and general configuration similar to those of the water
drainage layer or channel. Both layer types function to transmit preferen-
tially. The position in the cover system is a main distinction. The gas
drainage layer is placed on the lower side (Figure 19) to intercept gases
rising from waste cells, whereas the drain for water is positioned on the
upper side to intercept water percolating from the surface.
LOAM (FOR VEGETATION)
ff4ooooooooooooBLfUftu6u(ji/uiJui5ul)UlJUWlJuflU6
OOOOOOOOOOOOOOOOOO~~'*~ -- -- — ~~ ~ --- -~~
OOOOOOOOOOOOOOOOOO
000000000000000000
'BARRIER) '/////////
'2OOOOOOOOOOOOOOOOO
>OOOOOOOOOOOOOOOOO
,00000000000000000
OOOOOOOOOOOOOOOOOO
O o OO OO OO OOOOOC -----
OOOOOOOC -
oooooooooooooooooooooooooooooooooo
Figure 19. Cover layering suitable for
conveying gases to vents.
Evaluate Topsoil
Step 16
A topsoil or a subsoil made amenable to supporting vegetation fre-
quently forms the top of a layered cover system. Untreated subsoils are
seldom suitable directly, so it has been necessary frequently to supplement
35
-------
subsoil with fertilizers, conditioners, etc., as explained elsewhere
(Steps 26-28), to obtain the desired result. Loams or USCS types GM, GC,
SM, SC, ML, and CL (Figure 3) are recommended, but agronomic considerations
usually prevail. The upper lift should be placed in a loose condition and
not compacted.
Evaluate Time of Construction Step 17
Better results in placement of cover can often be achieved at certain
times (seasons) of the year. For this reason, the permit application may
need to have the time of cover construction bracketed. The dominant consid-
eration is commonly the season appropriate to establishing vegetation, and
the subject is discussed in more detail in Steps 31 and 32. The presence of
snow or a condition of frozen soil and waste interferes with proper place-
ment in many northern states. Later, the spring thaw can produce temporary
problems in handling and control of wet soil. On the other hand, hot, dry
summer weather can create construction problems of excessive drying and
cracking, wind erosion, and dust generation. As general guidance, it is
usually preferable to place cover in the spring or early fall (and to a
lesser degree through the summer). Departures from the two preferred inter-
vals should be justified in the application.
Review Proposed Construction Techniques Step 18
The application should be carefully reviewed for conformance to the
following general recommendations for layering (from the bottom up):
a. Make buffer layer below barrier thick and dense enough to provide
smooth, stable base for compacting in c below.
b. Compact all layers except topsoil and top lift of upper buffer.
c. In barrier layer, consider striving for 90 percent of maximum dry
density according to 5- or 15-blow compaction test where solid waste is soft
or according to standard 25-blow compaction test where solid waste is gran-
ular and soil-like.
d. Cover barrier layer soon enough to prevent excessive drying
and cracking.
e. Provide sufficient design thickness to assure performance of layer
function; specifying a 6- to 12-inch minimum should prevent excessively thin
spots resulting from poor spreading techniques.
f. Construct in plots small enough to allow rapid completion.
g. Consider seeding topsoil at time of spreading.
CONFIGURATION EVALUATION PROCEDURE
The concern for the configuration of the cover surface is driven
mostly by a desire to avoid excessive erosion or excessive infiltration.
36
-------
Not only is erosion objectionable in itself but erosion can degrade the
cover and seriously reduce its effectiveness.
Evaluate Erosion Potential
Step 19
The USDA universal soil loss equation (USLE) is a convenient tool for
use in evaluating erosion potential. The USLE predicts average annual soil
loss as the product of six quantifiable factors. The equation is:
A = RKLSCP
where A = average annual soil loss, in tons/acre
R = rainfall and runoff erosivity index
K = soil erodibility factor, tons/acre
L = slope-length factor
S = slope-steepness factor
C = cover-management factor
P = practice factor
The data necessary as input to this equation are available to the evaluator
in a figure and tables included below. Note that the evaluations in Step 8
on soil composition and Steps 25-32 on vegetation all impact on the evalu-
ation of erosion also.
Factor R in the USLE can be calculated empirically from climatological
data. For average annual soil loss determinations, however, R can be ob-
tained directly from Figure 20. Factor K, the average soil loss for a given
Figure 20. Average annual values of rainfall-erosivity factor R.
37
-------
soil in a unit plot, pinpoints differences in erosion according to differ-
ences in soil type. Long-term plot studies under natural rainfall have pro-
duced K values generalized in Table 5 for the USDA soil types.
TABLE 5. APPROXIMATE VALUES OF FACTOR K FOR
USDA TEXTURAL CLASSES11
Texture class
Sand
Fine sand
Very fine sand
Loamy sand
Loamy fine sand
Loamy very fine sand
Sandy loam
Fine sandy loam
Very fine sandy loam
Loam
Silt loam
Silt
Sandy clay loam
Clay loam
Silty clay loam
Sandy clay
Silty clay
Clay
Organic
O. 5$
K
0.05
.16
.1*2
.12
.21*
.1*1*
.27
-35
.1*7
.38
.1*8
.60
.27
.28
.37
.Ik
.25
0
matter content
2%
K
0.03
.11*
.36
.10
.20
.38
.21*
-30
.1*1
.31*
' .1*2
.52
.25
.25
.32
.13
.23
.13-0.29
k%
K
0.02
.10
.28
.08
.16
.30
.19
.21*
.33
.29
-33
.•1*2
.21
.21
.26
.12
.19
The values shown are estimated averages of broad
ranges of specific-soil values. When a texture is
near the borderline of two texture classes, use
the average of the two K values.
The evaluator must next consider the shape of the slope in terms of
length and inclination. The appropriate LS factor is obtained from Table 6.
A nonlinear slope may have to be evaluated as a series of segments, each with
uniform gradient. Two or three segments should be sufficient for most engi-
neered landfills, provided the segments are selected so that they are also
of equal length (Table 6 can be used, with certain adjustments). Enter
Table 6 with the total slope length and read LS values corresponding to the
percent slope of each segment. For three segments, multiply the chart LS
values for the upper, middle, and lower segments by 0.58, 1.06, and 1.37,
respectively. The average of the three products is a good estimate of the
38
-------
TABLE 6. VALUES OF THE FACTOR LS FOR SPECIFIC
COMBINATIONS OF SLOPE LENGTH AND STEEPNESS11
% Slope
0.5
1
2
3
4
5
6
8
10
12
14
16
18
20
25
30
40
50
60
Slope length (feet)
25
0.07
0.09
0.13
0.19
0.23
0.27
0.34
0.50
0.69
0.90
1.2
1.4
1.7
2.6
3.0
4.0
6.3
8.9
12.0
50
0.08
0.10
0.16
0.23
0.30
0.38
0.48
0.70
0.97
1.3
1.6
2.0
2.4
2.9
4.2
5.6
9.0
13.0
16.0
75
0.09
0.12
0.19
0.26
0.36
0.46
0.58
0.86
1.2
1.6
2.0
2.5
3.0
3.5
5.1
6.9
11.0
15.0
20.0
100
0.10
0.13
0.20
0.29
0.40
0.54
0.67
0.99
1.4
1.8
2.3
2.8
3.4
4.1
5.9
8.0
13.0
18.0
23.0
150
0.11
0.15
0.23
0.33
0.47
0.66
0.82
1.2
1.7
2.2
2.8
3.5
4.2
5.0 '
1.2
9.7
16.0
22.0
28.0
200
0.12
0.16
0.25
0.35
0.53
0.76
0.95
1.4
1.9
2.6
3.3
4.0
4.9
5.8
8.3
11.0
18.0
25.0
--
300
0.14
0.18
0.28
0.40
0.62
0.93
1.2
1.7
2.4
3.1
4.0
4.9
6.0
7.1
10.0
14.0
22.0
31.0
--
400
0.15
0.20
0.31
0.44
0.70
1.1
1.4
2.0
2.7
3.6
4.6
5.7
6.9
8.2
12.0
16.0
25.0
--
--
500
0.16
0.21
0.33
0.47
0.76
1.2
1.5
2.2
3.1
4.0
5.1
6.4
7.7
9.1
13.0
18.0
28.0
--
--
600
0.17
0.22
0.34
0.49
0.82
1.3
1.7
2.4
3.4
4.4
5.6
7.0
8.4
10.0
14.0
20.0
31.0
--
800
0.19
0.24
0.38
0.54
0.92
1.5
1.9
2.8
3.9
5.1
6.5
8.0
9.7
12.0
17.0
23.0
--
1000
0.20
0.26
0.40
0.57
1.0
1.7
2.1
3.1
4.3
5.7
7.3
9.0
11.0
13.0
19.0
25.0
--
Values given for slopes longer than 300 teet or steeper than 18% are extrapolations beyond the range of the research data and,
therefore, less certain than the others.
overall effective LS value.
0.71 and 1.29.
If two segments are sufficient, multiply by
Factor C in the USLE is the ratio of soil loss from land cropped under
specified conditions to that from clean-tilled, continuous fallow. There-
fore, C combines effects of vegetation, crop sequence, management, and agri-
cultural (as opposed to engineering) erosion-control practices. On land-
fills, freshly covered and without vegetation or special erosion-reducing
procedures of cover placement, C will usually be about unity. Where there
is vegetative cover or significant amounts of gravel, roots, or plant resi-
dues or where cultural practices increase infiltration and reduce runoff
velocity, C is much less than unity. Estimate C by reference to Table 7 for
anticipated cover management, but also consider changes that may take place
in time. Meadow values are usually most appropriate. See Reference 1 for
additional guidance.
Factor P in the USLE is similar to C except that it accounts for addi-
tional erosion-reducing effects of land management practices that are super-
imposed on the cultural practices, e.g., contouring, terracing, and contour
strip-cropping. Approximate values of P, related only to slope steepness,
39
-------
TABLE 7. GENERALIZED VALUES OF FACTOR C FOR STATES
EAST OF THE ROCKY MOUNTAINS11
#
Qop, rotation, and management
Base value: continuous fallow, tilled up and down slope
CORN
C, RdR, fallTP, conv
C, RdR, spring TP, conv
C, RdL. fall TP, conv
C, RdR, we seeding, spring TP, conv
C, RdL, standing, spring TP, conv
C-W-M-M, RdL, TP for C, disk tor W
C-W-M-M-M, RdL, TP for C, disk for W
C, no-till pi in c-k sod, 95-80% re *
COTTON
Cot, conv (Western Plains)
Cot, conv (South)
MEADOW
Grass & Legume mix
Alfalfa, lespedeza or Sericia
Sweet clover
SORGHUM, GRAIN (Western Plains)
RdL, spring TP, conv
No-till pi in shredded 70-50% re
SOYBEANS
B, RdL, spring TP, conv
C-B, TP annually, conv
B, no-till pi
C-B, no-till pi, fall shred C stalks
WHKAT
W-F, fall TP after W
W-F, stubble mulch, 500 Ibs re
W-F, stubble mulch, 1000 Ibs re
Productivity level
High
Mod.
C value
1.00
0.54
.50
.42
.40
.38
.039
.032
.017
0.42
.34
0.004
.020
.025
0.43
.11
0.48
.43
.22
.18
0.38
.32
.21
1.00
0.62
.59
.52
.49
.48
.074
.061
.053
0.49
.40
0.01
0.53
.18
0.54
.51
.28
.22
Abbreviations defined:
B - soybeans
C - corn
c-k - chemically killed
conv - conventional
cot - cotton
F - fallow
M - grass & legume hay
pi - plant
W -wheat
we - winter cover
Ibs re - pounds of crop residue per acre remaining on surface after new crop seeding
% re - percentage of soil surface covered by residue mulch after new crop seeding
70-50% re - 70% cover for C values in first column; 50% for second column
RdR - residues (corn stover, straw, etc.) removed or burned
RdL - all residues left on field (on surface or incorporated)
TP - turn plowed (upper 5 or more inches of soil inverted, covering residues)
40
-------
are listed in Table 8. These values are based on rather limited field data,
but P has a narrower range of possible values than the other five factors.
TABLE 8. VALUES OF FACTOR P
11
Practice
Contouring (Pc)
Contour strip cropping (Psc)
R-R-M-M1
R-W-M-M
R-R-W-M
R-W
R-O
Contour listing or ridge planting
(Pel)
Contour terracing (Pj)2
No support practice
Land slope (percent)
1.1-2
2.1-7
7.1-12
12.1-18
18.1-24
(Factor P)
0.60
0.30
0.30
0.45
0.52
0.60
0.30
3 0.6/Vn
1.0
0.50
0.25
0.25
0.38
0.44
0.50
0.25
0.5/\/n
1.0
0.60
0.30
0.30
0.45
0.52
0.60
0.30
0.6/V^"
1.0
0.80
0.40
0.40
0.60
0.70
0.80
0.40
0.8/VrT
1.0
0.90
0.45
0.45
0.68
0.90
0.90
0.45
0.9/Vn"
1.0
1 R = rowcrop, W = fall-seeded grain, O = spring-seeded grain, M = meadow. The crops are grown in rotation and so arranged on
the field that rowcrop strips are always separated by a meadow or winter-grain strip.
2 These P( values estimate the amount of soil eroded to the terrace channels and are used for conservation planning. For prediction
of off-field sediment, the Pf values are multiplied by 0.2.
3 n = number of approximately equal-length intervals into which the field slope is divided by the terraces. Tillage operations must
be parallel to the terraces.
Example: An owner/operator proposes to close one sec-
tion of his small landfill with a sandy clay subsoil
cover having the surface configuration shown in Fig-
ure 21. The factor R has been established as 200 for
this locality. The evaluator questions anticipated
erosion along the steep side and assigns the following
values to the other factors in the USLE after inspecting
Tables 5 through 8:
K = 0.14 LS = 8.3
C = 1.00
P = 0.90
The rate of erosion for the steep slope of the landfill
is calculated as follows:
A = 200 (0.14 tons/acre) (8.3) (1.00) (0.90)
= 209 tons/acre
This erosion not only exceeds a limit recommended by the
permitting authority but also indicates a potential
41
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exposure of solid waste in that side of the landfill.
The evaluator therefore recommends that the owner/
operator review his plan of closure to reduce the poten-
tial erosion. One way that the operator might accomplish
this reduction in erosion is by placing additional solid
waste along the steep slope in an overlapping wedge as
indicated in the figure. Although the new cover would
have a greater slope length, the overall effect is to
reduce the factor LS and the amount of erosion.
AS PROPOSED.
100 FEET
Figure 21. Hypothetical landfill configuration and modification.
Evaluate Surface Slope Inclination
Step 20
Rainfall runoff is increased by increases in inclination of the sur-
face, and accordingly, infiltration is decreased. Since erosion also in-
creases with increasing inclination (Step 19), the balance between these
opposing considerations often must be carefully evaluated. On slopes of
less than 3 percent, the irregularities of the surface and vegetation com-
monly act as traps for detention of runoff. The value 5 percent has been
suggested and used in grounds maintenance^ as an approximation of an incli-
nation sufficient to facilitate runoff without risking excessive erosion. A
quantitative evaluation of the erosional effect of inclination is outlined
for factor LS under Step 19.
Not only is erosion more serious as inclination is increased, but
slope mass stability can become a factor on relatively steep side slopes of
landfills and surface impoundments. Usually the evaluator will do well to
seek assistance from technical agencies experienced in analyzing slope sta-
bility since varied strength properties and seepage conditions can greatly
complicate the mass stability. As a rough guide, however, the evaluator can
usually count on the rule of thumb that not exceeding IV (vertical) on 4H
(horizontal) or other inclination shown by experience or analysis to be
relatively stable would assure satisfactory slope performance in most cases.
42
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The vulnerability of knoll-like configurations to wind erosion can be
evaluated by the use of Figure 22. An adjustment factor is obtained as an
erosion loss percentage of 100 or more in comparison with erosion loss from
a similar flat surface. This factor should be used to estimate the effects
of sides of landfills that may present a knoll-like configuration toward the
prevailing winds.
600
500
£400
g
1300
250
200
ISO
IOO
T
1-5 2 25 3 456
WINDWARD KNOLL SLOPE (PERCENT)
8 10
Figure 22. Knoll adjustment (a) from top
of knoll and (b) from upper
third of slope. -^ (Reproduced
by permission of Soil Science
Society of America.)
Another general rule of thumb provides that IV on 2H is the maximum
slope on which vegetation can be established and maintained, assuming ideal
soil with low erodibility and adequate moisture-holding capacity. In soils
less than ideal, maximum vegetative stability cannot be attained on slopes
steeper than about IV on 3H. Optimum vegetative stability generally re-
quires slopes of IV on 4H or flatter. Similarly, there are limits to the
inclination where mowing maintenance is planned. The limit can be as low as
IV on 6H for grassed ditches where two slopes meet at the bottom, but more
commonly the limit is about IV on 3H.
DRAINAGE EVALUATION PROCEDURE
Check Overall Surface Drainage System
Step 21
Examine the documentation to establish that drainage of surface runoff
from the covered area and surroundings has been thoroughly addressed. Maps
presenting topography or other descriptions of surface configuration should
be carefully reviewed to see that rainfall or snow melt on any'part of the
site is free to move downslope without encountering obstacles that might
43
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lead to ponding or excessive erosion. At the same time, a check should be
made to see that the slope is not anywhere in excess of the slopes for flat
surfaces and for ditches provided in the regulations. In those places such
as the edge of the landfill where slopes may of necessity be relatively
steep, a check for adverse effects in the form of excessive erosion should
be made as explained elsewhere (Step 19).
Evaluate Ditch Design Step 22
To confirm the adequacy of drainage ditches, the evaluator should for-
mally check the hydraulic calculations on which design for ditch cross sec-
tions are based. This step can be important but for many landfills may only
be necessary where diversion ditches convey runoff from beyond the site
around its edge. Calculation should not usually be necessary on the landfill
cover itself unless an overflow situation would have serious consequences.
Design (and evaluation) of a ditch is routinely accomplished using the
Rational equation (Step 7) and Manning's equation. It was explained in Sec-
tion 2 that calculations of discharge Q for design storm or storms should be
included with the documentation supplied with the application for closure.
Q in cubic feet/second is used to calculate ditch cross sections in
Manning ' s equation :
1.486 AR2/3 S1/2
where n = coefficient of roughness
A = area, square feet
R = hydraulic radius, feet
S = energy gradient, feet/ foot
The Manning's n value is usually obtained from a table and that author
itative reference should be cited in the application to facilitate checking.
For a rough check, use n = 0.02. The S in the equation is simply the lon-
gitudinal inclination of the ditch.
The design amounts to a manipulation of the remaining unknowns A and
R within certain constraints. Numerous tables have been developed and are
available for assistance in design; again these references should be identi-
fied when used. The cross-sectional area A of the waterfilled ditch is
affected by the choice of shape, e.g., between triangular and trapezoidal.
The hydraulic radius R is 'also affected since it is by definition the area
divided by the wetted perimeter formed by the ditch. A final constraint is
the requirement that erosion in the ditch be limited by limiting discharge
velocity Q/A to an appropriate maximum from among those determined as crit-
ical for the range of soil types (Table 9).
Evaluate Culvert Design Step 23
Evaluations of culverts and other closed structures that may occasion-
ally be used as a part of the surface drainage system are approached in ap-
proximately the same way as Step 22. An added complication is the capacity
44
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TABLE 9. THRESHOLD VELOCITY FOR EROSION IN DITCHES
Soil V feet/second
max'
GP
GW,
GM
SC
SM
SW,
CL,
ML,
GC
SP
CH
MH
7-8
5-7
2-5
3-4
2-3
1-2
2-3
3-5
of the structure to transmit the water. Where the capacity is too small,
water will back up and form a pond, at least temporarily.
Check Gas Drainage Step 24
Municipal waste usually generates methane and carbon dioxide. Indus-
trial and hazardous wastes may also produce these gases and may contain suf-
ficient other volatile components to be of concern (see Step 11). Depending
on location, land use, and the proximity of buildings, there may be a need
for a careful review of the routes of gas drainage.* Methane leakage occa-
sionally threatens human life by potential for explosion. Volatile com-
pounds such as HCB and PCB may present a health or environmental problem.
More commonly landfill gases pose a serious threat to the success of vege-
tation in the long-term.16 Guidance on the best soils for blocking gas or,
at the other extreme, for conveying gas is given in Step 8. The effects of
water content, thickness, and layering of cover are discussed in Steps 11
and 15. What remains is commonly to connect the broad collecting layers to
surface vents, sometimes through linear drainage features consisting of
gravel-filled trenches in which perforated collector pipes are embedded.
See Step 15 for criteria on gravelly drains. Details of the system should
be submitted with the permit application and should include the features for
venting. Reference 17 reviews the passive and induced (pumped) venting
systems.
VEGETATION EVALUATION PROCEDURE
Rapid establishment and maintenance of vegetation can be accomplished
on soil covering solid waste only by carefully addressing soil type,
* Step 24 is unnecessary for wastes containing no garbage or volatile
chemicals.
45
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nutrient and pH levels, climate, species selection, mulching, and seeding
time.1 Fertile soils, if available at all for landfill cover, are usually
cost-prohibitive, so that nonproductive soils or subsoils often have to be
used. County agricultural agents can provide guidance based on local
conditions.
Evaluate Soil Suitability for Vegetation Step 25
Soil composed of a mixture of clay, silt, and sand such that none of
the components dominates is called a loam. The stickiness of the clay and
the floury nature of the silt are balanced by the nonsticky and mealy or
gritty characteristics contributed by the sand. A loam is rated overall
best for supporting vegetation as it is easily kept in good physical condi-
tion and is conducive to good seed germination and easy penetration by
roots.
Clay-rich soils may be productive when in a granular condition, but
they require special management methods to prevent puddling or breaking down
of the clay granules. Silt-rich soils lack the cohesive properties of clay
and the grittiness of sand, are water retentive, and usually are easily kept
in good condition. Soils made up largely of sand can be productive if suf-
ficient organic matter is present internally or as a surface mulch to hold
nutrients and moisture; sandy soils tend to dry out very rapidly and lose
nutrients by leaching.
Remember that worthwhile provisions in establishing vegetation may be
to stockpile and then to reuse the original topsoil. The less fertile under-
lying soil will be available as daily or intermediate cover. As the opera-
tion nears completion, the stockpiled topsoil can be used in the final cover
to facilitate growth of grasses and/or shrubbery. The original topsoil must
be significantly more fertile than underlying soil strata; otherwise, stock-
piling is not practical or economical.
Evaluate pH Level Step 26
Tests should be made to determine pH and buffering capacity (usually
stated as tons/acre of lime necessary to adjust the soil pH to around 6.5).
The amount of lime necessary to neutralize a given soil depends upon soil
pore-water pH and "reserve acidity." The reserve acidity is a single factor
which incorporates several variables; soils with high levels of organic
matter and/or clay require higher amounts of lime for pH adjustment. The pH
of subsoil (where appreciable in the cover) also influences lime require-
ments; acidic subsoils require higher levels and repetitive applications of
lime. Some buried landfill wastes act much like acid subsoils making higher
lime application levels or more frequent liming intervals necessary for ade-
quate pH control.
Evaluate Nitrogen and Organic Matter Step 27
Nitrogen is of special importance in establishing vegetation because
it is needed in relatively large amounts during vigorous growth but is easily
lost from the soil. Nitrogen fertilizer requirements depend upon the amount
46
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of organic matter present (higher organic matter levels requiring higher ap-
plication rates), the soil texture (more is required on sandy soils), and
the seed mixture chosen (more is required for grasses than legumes). Gener-
ally, 50 to 85 pounds/acre of nitrogen are recommended. Fertilizers are
rated by the amount of nitrogen they contain per weight of fertilizer (e.g.
6 percent nitrogen). To calculate the amount of fertilizer necessary to
furnish the recommended amount of nitrogen, simply divide the recommended
application by the fractional amount of nitrogen the fertilizer to be used
contains. For example, to apply 50 pounds/acre of nitrogen using fertilizer
which is 6 percent nitrogen, divide 50 by 0.06 to get 833 pounds/acre of
fertilizer required. Table 10 indicates typical ranges of organic matter in
different soil types and a rough range of nitrogen levels present in a typi-
cal loam with moderate levels of organic matter.
Evaluate Other Nutrients
Step 28
Necessary levels of phosphorus in soil are shown in Table 10. Unlike
TABLE 10. RELATIVE LEVELS OF ORGANIC MATTER AND MAJOR NITRIENTS IN SOILS18
Organic Matter,
Relative
Level*
Very low
Low
Medium
High
Very
high
Sand,
Loamy
Sand
<0.6
0.6-1.5
1.6-2.5
2.6-3.5
>3.5
Sandy Loam,
Loam,
Silt Loam
<1.6
1.6-3.0
3.1-U.5
U. 6-5.5
>5.5
percent
Clay Loam,
Sandy Clay,
Clay
<2.6
2. 6-1*. 5
U.6-6.5
6.6-7.5
>7.5
Nitrogen
Ib/acre
<20
20-50
50-85
85-125
>125
Phosphorus
Ib/acre
<6
6-10
11-20
21-30
>30
Potassium
Ib/acre
<6o
60-90
91-220
221-260
>260
* Medium level is typical of agricultural loam soil. Low levels need supple-
mental fertilization; high levels need no fertilization under normal
circumstances.
nitrogen, phosphorus is not mobile in the soil and thus is lost very slowly
to leaching. It is possible to give enough phosphorus in one application to
last several growing seasons. Generally at least 15 pounds/acre of phos-
phorus* is recommended as a starter. The availability of phosphorus to the
plant is quite dependent on pH. At optimum pH values (6.2-6.8), amounts of
50 pounds/acre are usually adequate; at pH values below 6.2 or between 6.9
and 7.5, about 80 pounds/acre is needed for optimum growth. Under very al-
kaline conditions (pH greater than 7.5), phosphorus levels of 110 pounds/acre
are required. These recommendations are for raw subsoils, or for sandy or
high clay soils of low organic material content.
* In calculating on the basis of P 0 , remember that percent P,^,. is 2.3 times
an equivalent percent phosphorus.
47
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Potassium is much less important in grass establishment than in legume
establishment and maintenance; thus the rate of application depends upon both
test results and species to be seeded. A minimum potassium application of
26 pounds/acre (32 pounds/acre of K_0) as a starter is recommended under any
circumstances. Potassium applications can run as high as 230 pounds/acre
(277 pounds/acre of K?0) on impoverished soils where legumes are to be
seeded. Potassium is moderately mobile in the soil and is slowly leached
out, but one heavy application should be adequate for several growing
seasons.
Evaluate Species Selection Step 29
Each species of grass, legume, shrub, or tree has its own environmental
and biological strengths and limitations. Moisture, light, temperature, ele-
vation, aspect, balance and level of nutrients, and competitive cohabitants
are all parameters which favor or restrict plant species. The selection of
the best plant species for a particular site depends upon knowledge of
adapted plants that have the desired characteristics. Table 11 gives the
major parameters usually important to species selection and examples of
grasses and legumes' exhibiting the parameters. Characteristics which almost
universally should be given precedence are: low growing and spreading from
rhizomes or stolons; rapid germination and development; and resistance to
fire, insects, and disease. Plants which are poisonous or are likely to
escape the site and become noxious should be avoided.
A very large number of species of grasses and legumes are available
for reclamation use. Species that find wide and frequent application are
described in Tables 12 and 13. A local agronomist should be consulted for
recommendation of locally adapted plant varieties.
Evaluate Shrubs and Trees Step 30
Volunteer and native species of shrubs and trees tend to invade land-
fill cover systems^" mucn as they will any disturbed land. The extreme en-
vironment of the cover may be less restrictive to certain strong species of
shrubs and trees, and the astute planner or reviewer should allow for or
even take advantage of such relative strengths that would appear in the
future. One planning strategy is to specify the planting of the preferred
volunteer species at the start. Otherwise, more control of species taking
root in the future may be necessary (Step 34). Actually, the growth of
shrubs and trees may be an unfavorable development because of the effects of
their deep roots on the integrity of the cover. Besides its importance to
planning for post-closure care this development also needs to be considered
in assessing risks posed by the facility after the extended care terminates.
The special conditions of greatest concern in maintaining healthy
shrubs and trees are often the thinness and intermittent dryness of the
cover soil.16 The adverse consequence of thinness is that only small,
shallow-rooted species may survive, and even some of these will become un-
stable and will topple during winds. Where planted shrubs and trees warrant
high priority, it may be necessary to assure success by providing a wide,
deep pocket of soil around each plant.
48
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TABLE 11. IMPORTANT CHARACTERISTICS OF GRASSES AND LEGUMES
Characteristic
Degree *
Common Examples
Texture Fine Kentucky bluegrass, bentgrass, red fescue
Coarse Smooth bromegrass, reed canarygrass,
timothy
Growth height Short Kentucky bluegrass, buffalograss, red fescue
Medium Redtop, perennial ryegrass
Tall , Smooth bromegrass, timothy, switchgrass
Growth habit Bunch Timothy, big bluestem, sand dropseed,
perennial ryegrass
Sod former Quackgrass, smooth bromegrass, Kentucky
bluegrass, switch1 grass
Reproduction Seed Red and alsike clover, sand dropseed, rye,
perennial ryegrass, field bromegrass
Vegetative Prairie cordgrass, some bentgrasses
Seed and White clover, crownvetch, quackgrass,
vegetative Kentucky bluegrass, smooth bromegrass
Annual Summer Rabbit clover, oats, soybeans, corn,
sorghum
Winter Rye, hairy vetch, field bromegrass
Perennials Short-lived Timothy, perennial ryegrass, red and
white clover
Long-lived Birdsfoot trefoil, crownvetch, Kentucky
bluegrass, smooth bromegrass
Maintenance Difficult Tall fescue, reed canarygrass, timothy,
alfalfa
Moderate Kentucky bluegrass, smooth bromegrass
Easy Crownvetch, white clover, birdsfoot
trefoil, big bluestem
Shallow rooted Weak Sand dropseed, crabgrass, foxtail, white
clover
Strong Timothy, Kentucky bluegrass
Deep rooted Weak Many weeds
Strong Big bluestem, switchgrass, alfalfa, reed
canarygrass
Moisture Dry Sheep fescue, sand dropseed, smooth
bromegrass
Moderate Crested wheatgrass, red clover
Wet Reed canarygrass, bentgrass
Temperature Hot Lehman lovegrass, fourwing saltbush,
ryegrass
Moderate Orchard grass, Kentucky bluegrass, white
clover
Cold Alfalfa, hairy vetch, smooth bromegrass,
slender wheatgrass
* Variety, specific characteristic, subcharacteristic, or
favored condition.
49
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Example: A local agronomist has recommended that gray
birch (a volunteer species) be planted on the cover for
a landfill in New England. The reviewer asks for clari-
fication in the plan on the development of roots for the
expected tree density. This information will help the
reviewer to evaluate the likely changes in effectiveness
of the cover for impeding percolation.
Evaluate Time of Seeding
Step 31
Probably the most critical of all decisions in the successful estab-
lishment of vegetative cover on poor soils is the time of seeding. The opti-
mum time of seeding depends on the species selected and the local climate.
Best seeding time under normal circumstances is presented in Tables 12 and
13 for the recommended grasses and legumes. A local county agent or seed
house should be consulted for more specific local information. Note the
interrelationship with Step 17-
Most perennials require a period of cool, moist weather to become es-
tablished to the extent that they can withstand a cold winter freeze or hot
summer drought. Early fall (late August in the north through October in the
south) usually allows enough time for the plants to develop to the stage
that they can withstand a hard winter. Plants then have a good start for
TABLE 12. GRASSES COMMONLY USED FOR REVEGETATION*
Variety
Redtop bentgrass
Smooth bromegrass
Field bromegrass
Kentucky bluegrass
Tall fescue
Meadow fescue
Orchard grass
Annual ryegrass
Timothy
Best
Seeding
Time
Fall
Spring
Spring
Fall
Fall
Fall
Spring
Fall
Fall
Seed Densityt
seeds/ft2
ll»
2.9
6.H
50
5.5
5.3
12
5.6
30
Important Characteristics
Strong, rhizomatous roots,
perennial
Long-lived perennial
Annual, fibrous roots,
winter rapid growth
Alkaline soils, rapid grower,
perennial
Slow to establish, long-lived
perennial, good seeder
Smaller than tall, susceptible
to leaf rust
More heat tolerant but less
cold resistant than smooth
bromegrass or Kentucky bluegrass
Not winter hardy, poor dry
land grass
Shallow roots, bunch grass
Areas /Conditions
of Adaptation
Wet, acid soils, warm
season
Damp , cool summers ,
drought resistant
Cornbelt eastward
North, humid U.S.
south to Tennessee
Widely adapted, damp
soils
Cool to warm regions,
widely adapted
Temperate U.S.
Moist southern U.S.
Northern U.S., cool,
Reed canarygrass
Late 13 Tall coarse, sod former,
summer perennial, resists flooding
and drought
humid areas
Northern U.S., wet,
cool areas
* Taken from many sources, but especially References 18 and 19.
t Number of seeds per square foot when applied at 1 pound/acre,
50
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TABLE 13. LEGUMES COMMONLY USED FOR REVEGETATION*
Variety
Alfalfa (many varieties)
Birds foot trefoil
Sveet clover
Red clover
Alsike clover
Korean lespedeza
Sericea lespedeza
Hairy vetch
White clover
Crownvetch
Best
Seeding
Time
Late
summer
Spring
Spring
Early
spring
Early
spring
Early
spring
Early
spring
Fall
Early
fall
Early
fall
Seed Densityt
seeds/ft2
5.2
9.6
6.0
6.3
16
5.2
8.0
0.5
18
2.7
Important Characteristics
Good on alkaline loam, re-
quires good management
Good on infertile soils,
tolerant to acid soils
Good pioneer on non-acid soils
Not drought resistant,
tolerant to acid soils.
Similar to red clover
Annual, widely adapted
Perennial, tall erect plant,
widely adapted
Winter annual, survives below
0°F, widely adapted
World-wide, many varieties,
does well on moist, acid soils
Perennial, creeping stems and
rhizomes, acid tolerant
Areas /Conditions
of Adaptation
Widely adapted
Moist, temperate
U.S.
Widely adapted
Cool, moist areas
Cool, moist areas
Southern U.S.
Southern U.S.
All of U.S.
All of U.S.
Northern U.S.
* Taken from many sources, but mainly from References 18 and 19.
t Number of seeds per square foot when applied at 1 pound/acre.
early spring growth and can reach full development before any* summer drought.
Spring planting is usually second choice for all but a few of the more
rapidly developing perennials. Germination and early development are slowed
due to the cool early spring weather. Late frosts often severely damage the
young plants. Late spring planting does not allow enough time for most pe-
rennials to mature before summer, and annuals will usually outcompete the
preferred perennials.
Annuals generally are best planted in spring and early summer. Growth
is completed quickly prior to the summer heat and before the soil moisture
is used up. During this period annuals easily outcompete the perennials.
Annuals can, however, be planted any time the soil is damp and warm when a
quick plant cover is desired and often will provide an acceptable mulch for
fall-seeded perennials.
Evaluate Seed and Surface Protection
Step 32
Bare soil as a seeding medium suffers from large temperature and mois-
ture fluctuations and from rapid degeneration due to wind and water erosion.
Mulches provide temporary protection against these influences; therefore,
the use of mulch should be expected in the plan for closure cover.
Almost any material spread, formed, or simply left on the soil surface
will act as a mulch, e.g., straw and other crop residues, sawdust, wood
chips, wood fiber, bark, manure, brush, jute or burlap, gravel, stones,
51
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peat, paper, leaves, plastic film, and various organic and inorganic li-
quids. For straw used where erosion is not anticipated, an application of
1.5 tons/acre is recommended. On slopes or elsewhere where erosion threat-
ens, 2 tons/acre produces better results. Application rates over 2.5 tons/
acre often result in reduced germination and emergence and such high rates
should be avoided.
Rapid growing, summer cover crops can be used to advantage as living
mulches if final grade work is finished in late spring or early summer when
chances of successful perennial grass-legume seedings are low. Coarse
grasses such as Sudan grass or a local equivalent are good choices as they
are widely adaptable, and the tall, stiff stalks are most effective as a
mulch.
Petroleum-based products such as asphalt and resins are often suitable
and are frequently used as mulching materials. Specially formulated emul-
sions of asphalt under various trade names have been used throughout the
world to prevent erosion, reduce evaporation, promote seed germination, and
warm the soil to advance the seeding date. The film clings to but does not
deeply penetrate the soil; it is not readily destroyed by wind and rain and
remains effective from 4 to 10 weeks. Application rates of 1000-1200 gallons/
acre are usually required to control erosion. Asphalt mulches cost about
twice the applied cost of a straw mulch.
52
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SECTION 4
POST-CLOSURE PLAN
Provisions for maintenance and for contingencies after site closure
should follow a logical plan.
MAINTENANCE EVALUATION PROCEDURE
Some cover deterioration like erosion can be tolerated where the post-
closure plan has provisions for frequent, regular maintenance. Elsewhere
regular maintenance of the cover may be planned on a less frequent interval,
in which case a more conservative cover design is necessary at the start.
Evaluate Design/Maintenance Balance Step 33
Check to see that the plan for closure covering generally achieves a
reasonable balance between initial design and plans for monitoring, mainte-
nance, and repair. So many specific factors (climate, waste type, soil,
vegetation, etc.) are involved in evaluating this balance that little de-
tailed guidance can be offered; nevertheless, the assessment is important
and should be performed with care and diligence. The following example
helps clarify the general nature of the problem and the recommended
philosophy.
Example: In a late modification, the applicant formally
proposes to reduce the frequency of post-closure moni-
toring inspection visits to a remote hazardous waste
site by overdesigning the closure cover at the start. A
certain period between inspection visits has become more
or less standard in the region on the basis of experi-
ence, but the applicant now proposes to double this
period. The overdesign amounts to prescribing a thicker
cover than might ordinarily be considered sufficient.
In this case the evaluator rejects the proposed modifi-
cation of less frequent inspections. He reasons that
emergency conditions, such as from wind or water erosion
or from cover cracking, can compound and intensify the
problem in a short period in this region; therefore,
frequent inspections are imperative and necessary.
Evaluate Maintenance of Vegetation Step 34
After vegetation is established on a landfill, maintenance is neces-
sary to keep less desirable, native species from taking over and weak areas
53
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in the cover from developing. In most areas judicious, twice-yearly mowing
will keep down weed and brush species. Annual fertilization (and liming if
necessary) will generally allow desirable species to outcompete the weedy
species of lower quality. Occasional use of selective herbicides usually
controls noxious invaders, but care must be taken to avoid injuring or weak-
ening the desirable species, lest more harm than benefit results in the
long run. In rare circumstances, large insect populations may threaten the
stand of vegetation so that insecticide application becomes desirable. The
evaluator should review the intermediate and long-range plans for maintain-
ing vegetation with cognizance of plant needs in establishment (and reestab-
lishment) as outlined in Steps 26-32.
Landfill cover soils are usually shallow and of low quality for grow-
ing high-quality vegetation. This problem is greatly compounded if an im-
pervious clay or plastic barrier is incorporated in the cover. Such a bar-
rier makes the plant-root zone susceptible to swamping after moderate rains
since vertical drainage is impeded. Upon saturation, the soil becomes an-
aerobic and roots in the system are threatened. Short periods of swamping
will weaken the vegetation; longer periods may cause a complete loss. Swamp-
ing tolerant species (such as reed canarygrass) and surface drainage will
lessen these problems.
On the other extreme, thin layers dry excessively during droughty pe-
riods. No deep soil moisture is available to tide the plants over even mod-
erate droughts. Plants which have been weakened by prior waterlogging or
that are not drought-tolerant are especially vulnerable. Irrigation may be
necessary during prolonged dry spells to preclude complete loss of plant
cover.
Landfills may continue to produce gases and soluble organic decomposi-
tion products for years after closure, and vegetation can be damaged. An
impervious cover keeps the landfill dry so that gas production is low or non-
existent and also may shield the plant roots from these products. Deep-
rooted shrubs or trees are usually not recommended on landfills since roots
will tend to penetrate into the waste zone.
Evaluate Provisions for Condition Surveys Step 35
Applications for closures should include plans for monitoring the site
in the future. An annual site visit by a technical person qualified to eval-
uate the condition of the cover may be considered sufficient by the permit-
ting authority for some sites. Elsewhere, however, it may be judged that
more frequent inspections are necessary. Provisions should be made in the
application for collecting documentation during the site visit. The docu-
mentation and inspection reports should be kept on site by the owner/
operator or at some other location where it can be examined conveniently.
Copies of the reports including all significant observations or conclusions
should be kept in the applicant's file for review on request by the oversee-
ing agency.
Example: The evaluator has reviewed an application for
closing a site and found that there is sufficient
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planning to monitor site conditions over an extended
period. He notes, however, that the site visits are to
be made by a representative of the owner/operator with
no provision for a state or EPA representative to accom-
pany the inspector. Among changes he requires in this
application, therefore, is the stipulation in the post-
closure plan that the state agency (or EPA) will be
notified five days before the site visit so that they
may send a representative.
CONTINGENCY PLAN EVALUATION PROCEDURE
Evaluate Plan for Erosion Damage Repair Step 36
Long-term maintenance helps to avoid erosion problems. However, un-
usual climate conditions and shortcomings in the design occasionally cause
excessive erosion by wind or water even on well-maintained covers.
Factors that need to be considered in the plan include the future
source of supply of fill soil for repair and the ability of someone to under-
take the repair work. The extent of repair work should be detailed in words
to the effect that repair work will bring lines and grades at least to their
original configuration. It is also appropriate to expect that the remedial
work will involve redesign where excessive erosion indicates that the orig-
inal design was deficient. Some of the many options that might be mentioned
for consideration in the case of a necessity for repair would include con-
struction of berms, protection of slopes and channels by riprap, and the use
of other special energy dissipators such as check dams.
In anticipation of major problems of sheet erosion across entire sur-
faces such methods as terracing might be identified, provided their effect
on infiltration is not excessively adverse.
In those regions where wind erosion can present a serious problem, the
post-closure plan should include specific statements on correcting wind ero-
sion problems. The following example is illustrative of the recommended
attitude.
Example: Consider a site in the southern Great Plains.
An applicant proposes to dispose of waste in a trench
operation in which soil excavated from the trench will
be used as final cover. Since a considerable mound will
have been formed upon closure, the evaluator foresees
the possibility of eventual wind erosion. No provision
with specifics for timely repair addresses this possible
erosion problem, so the evaluator recommends that the
applicant develop contingencies accordingly. The evalu-
ator offers for consideration the use of snow fences as
one quick response technique.
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Evaluate Plan for Vegetation Repair Step 37
Waste disposal areas have long-lived potential for negative impact,
and permanent vegetative cover should be maintained. Once a cover of vege-
tation is started and stabilized, extensive root systems develop and decom-
position processes form a layer of humus capable of perpetuating the cover
of vegetation. However, erosion forces, burrowing animals, etc., may damage
parts of this cover of soil, humus, and vegetation. Provisions should be
made for repairing such damage, specifically for transplanting grass sod,
planting the new seeds or shrubs, and replacing eroded soil during the in-
active life of the area.
The principal part of the application documents that the evaluator
should carefully review is that part dealing with measures to return damaged
vegetation to a state such as originally planned (see VEGETATION EVALUATION
PROCEDURE, SECTION 3). One additional concern of the plan for maintenance
of vegetation is that any deterioration of the vegetative cover is often
widespread; swampiness or droughtiness, nutrient starvation, or methane mi-
gration once appearing in the cover may quickly affect the entire vegetation
system. Exceptions are problems induced by erosion, and repair in this case
should be of less concern. Because of this potential widespread impact the
applicant's plans for maintaining or for repairing the vegetation should be
closely tied to the monitoring plan and should be adequate to respond quickly
to the early stages of a developing problem.
Evaluate Plan for Drainage Renovation Step 38
The principal part of the applicant's plan for drainage renovation
should include sufficient details to assure that the drainage system for the
site as designed will be restored quickly to its original condition. Fur-
thermore, the plan for repair should provide for such additional work as
becomes necessary after a period of operations. Such additional work might
include repair of gullies and placement of riprap along a slope subjected to
more erosive action than anticipated in the original drainage design. Ex-
cept for such unexpected problems, the maintenance of drainage should amount
to fairly straightforward cleaning of ditches and cutting of brush.
Evaluate Provisions for Other Cover Deterioration Step 39
Contingency planning should include making provisions for all forms of
cover deterioration other than erosion and distress of the vegetation covered
elsewhere. The relatively high unit weights of some freshly compacted cover
soils will be reduced substantially in a few years. This bulking (brought
on partly by penetration of countless fine roots) benefits vegetation but
negatively affects the cover as a barrier to percolation. Other deteriora-
tion might result from deep root penetration, cracking, disturbance by cold
weather, seepage, and slope instability. The evaluator should consider the
likely effectiveness of post-closure plans to addressing such problems in a
timely manner. His evaluation should, of course, be made in the context of
policies established by state agencies and EPA. Such policies need not neces-
sarily assign responsibility for correcting such unanticipated problems to
the owner/operator.
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11. Stewart, B. A. et al., "Control of Water Pollution from Cropland:
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D. C., 1980. PB 81-166-365.
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New York, NY, 631 pp., 1977.
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Science Society of America Proceedings, Vol 29, pp. 602-608, 1965.
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Control Planning and Implementation," U. S. Environmental Protection
Agency, Report EPA-R2-72-015, Washington, D. C., 1972. PB 213-119/1BA.
16. Gilman, E. F. et al., "Guidelines for Plant Vegetation on Completed
Sanitary Refuse Landfills," U. S. Environmental Protection Agency,
Report (draft), Cincinnati, OH, 1981.
17- Pacey, J. G., "Controlling Landfill Gas," Waste Age, Vol 12, No. 3,
pp. 32-36, 1981.
18. Bennett, F. W. and Donahue, R. L., "Methods of Quickly Vegetating
Soils of Low Productivity," U. S. Environmental Protection Agency,
Report EPA-440/9-75-006, Washington, D. C., 1975. PB 253-329/7BA.
19. U. S. Department of Agriculture, "Grass, the Yearbook of Agriculture,"
House Document No. 480, 80th Congress, Washington, D. C., 1948.
*U.S. GOVERNMENT PRINTING OPFIOEl 1982-0-361-082/322
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